detection of biological warfare agents using ultra violet-laser induced fluorescence lidar

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx

Contents lists available at SciVerse ScienceDirect

Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

journal homepage: www.elsevier .com/locate /saa

Review Article

Detection of biological warfare agents using ultra violet-laser inducedfluorescence LIDAR

1386-1425/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.saa.2013.04.082

⇑ Corresponding author. Tel.: +91 11 23907539; fax: +91 11 23811319.E-mail address: [email protected] (R.C. Sharma).

Please cite this article in press as: D. Joshi et al., Detection of biological warfare agents using ultra violet-laser induced fluorescence LIDAR, SpectrocActa Part A: Molecular and Biomolecular Spectroscopy (2013), http://dx.doi.org/10.1016/j.saa.2013.04.082

Deepti Joshi, Deepak Kumar, Anil K. Maini, Ramesh C. Sharma ⇑Laser Science and Technology Centre, Metcalf House, DRDO, Delhi 110 054, India

h i g h l i g h t s

� System has application in earlywarning against biological warfareattack.� Review highlights the threat of

biological warfare agents, their types,and detection using UV-LIF LIDAR.� LIF signal of Bacillus globigii cloud at

distance up to 5 km is presented withMAPMT and ICCD detectors.� Overview of current research in

internationally available working UV-LIF LIDAR systems are also mentionedbriefly.� This review will be very useful for

graduate and under graduatestudents in understanding of StandoffUV-LIF LIDAR system.

g r a p h i c a l a b s t r a c t

UV-LIF LIDAR system.

a r t i c l e i n f o

Article history:Received 7 February 2012Received in revised form 11 April 2013Accepted 24 April 2013Available online xxxx

Keywords:Bacillus anthracisBiological warfare agentsLaser induced fluorescenceDepolarization LIDARUV-LIF LIDARHomeland security

a b s t r a c t

This review has been written to highlight the threat of biological warfare agents, their types and detec-tion. Bacterial biological agent Bacillus anthracis (bacteria causing the disease anthrax) which is mostlikely to be employed in biological warfare is being discussed in detail. Standoff detection of biologicalwarfare agents in aerosol form using Ultra violet-Laser Induced Fluorescence (UV-LIF) spectroscopymethod has been studied. Range-resolved detection and identification of biological aerosols by bothnano-second and non-linear femto-second LIDAR is also discussed. Calculated received fluorescence sig-nal for a cloud of typical biological agent Bacillus globigii (Simulants of B. anthracis) at a location of�5.0 km at different concentrations in presence of solar background radiation has been described. Over-view of current research efforts in internationally available working UV-LIF LIDAR systems are also men-tioned briefly.

� 2013 Elsevier B.V. All rights reserved.

Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Biological agents as weapon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Description of biological agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Bacterial-agents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

himica

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2 D. Joshi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx

PleaseActa P

Viral agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Rickettsiae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Biological toxins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Virulence factors of B. anthracis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Criteria for detection techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Fluorescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Fluorophores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Tryptophan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Other fluorescent molecules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Principle of UV-LIF LIDAR system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Operation of the UV LIDAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Theoretical analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Evaluation of LIF LIDAR signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Parameters of UV-LIF LIDAR system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Solar background contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

International scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Introduction

In today’s world there is increasing awareness to vulnerabilitiesto biological attack not only to military assets but civilian targetsas well. The defense against the use of biological agents is a na-tional security and homeland defense objective. Use of biologicalagents as a means for defeating enemies has persisted throughthe centuries [1]. Following scientific breakthroughs such as theunderstanding of the germ theory of disease by Koch in the late19th century, bio-weapons found increased emphasis, withnumerous nation-state programs existing throughout the 20thcentury [2,3], and some into the 21st [4]. There is a long historicrecord of use of biological warfare (BW) agents. During WorldWar-I anthrax agent was used against human beings and animalsby Germans, followed by large scale field trials by Japanese againstwar prisoners and Chinese population during World War II. Biolog-ical program took back seat after Biological and Toxin WeaponConvention (BTWC) in 1972. But biological agents regained theirimportance after the bioterrorist attack of anthrax powder onOctober 4, 2001. United States experienced its most severe bio-at-tack when a perpetrator mailed anthrax spores to the news mediaand the Congress, resulting in 22 casualties, including five deaths[5]. Although US postal service was used for that attack but in fu-ture the bioterrorist attack can happen through aerosol route also.So there is a need to develop a system to provide early warning of aremote biological warfare attack so that protective measures canbe taken before getting exposed to infectious and lethal doses ofthe aerosol cloud.

Biological agents as weapon

Biological agents (BAs) are naturally occurring or engineeredbacteria, viruses, fungi, rickettsiae and biological toxins. The useof BAs as weapon is a serious threat because of several reasons [6].

(a) BAs have the ability to multiply in the human body and sig-nificantly increase their effect in contrast to their chemicalcounterparts.

(b) BAs are highly virulent and toxic; they have an incubationperiod (their effects are not seen even days after dissemina-tion) and some can be transmitted from person to person.

(c) Biological agents can be grown in facilities that are inexpen-sive to construct because all that is involved is growingorganisms that are found in nature in a lot of cases. There-

cite this article in press as: D. Joshi et al., Detection of biological warfareart A: Molecular and Biomolecular Spectroscopy (2013), http://dx.doi.or

fore biological agents have often being described as poorman’s bomb. BAs can be grown in facilities that resemblepharmaceutical, food or medical production sites that pro-vides no detectable sign that such agents are being pro-duced. In the absence of adequate detection system thereis time lag between infection and appearance of symptoms,which gives the perpetrators a chance to escape.

(d) BAs have remarkably low dose for infection (the quantity ofagents that is required to create desired results) in compar-ison to other types of agents. The approximate mass in mil-ligrams (mg) of a biological agent needed to achieve thedesired results in comparison to toxins and chemical war-fare agents is shown in Fig. 1.

A vast difference in effectiveness between biological agents(microbial agents, e.g., bacteria and viruses) and chemical agentscan be easily seen. As it is evident from the figure, some biolog-ical agents are as much as fourteen billion times dangerous incomparison to chemical agents. It can also be noted fromFig. 1 that if a terrorist chooses to use a toxin agent (in orderto get relatively rapid effects in a tactical situation), a muchgreater mass of the toxin agent will have to be employed thanif biological agents were being used under similar disseminationconditions. Though it is difficult to guess bioagents that can beused in biological warfare yet their selection may be based onthe following criteria [7–9].

1. Lethality.2. Ease of production in large quantities.3. Stability in aerosol form.4. Ease of dissemination.5. Contagiousness.6. Ability to impact public health, causing panic and social

disruption.7. Unavailability of treatment or vaccine.

Based on above criteria, biological agents, which are consideredof great concern, are summarized in the Table 1 below:

The bio-agent can be dispersed by various ways. Three majorways have been identified for their dissemination [10,11].

1. By vector (i.e. insects).2. Contaminating water or food supply.3. Distributing as bio-aerosol particles.

agents using ultra violet-laser induced fluorescence LIDAR, Spectrochimicag/10.1016/j.saa.2013.04.082


Fig. 1. Comparative toxicity of biological warfare (BW) agents, chemical warfare (CW) agents and Toxins.

D. Joshi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx 3

Although well known insects normally transmit virulent dis-eases for instance, fleas transmit plague and mosquitoes transmityellow fever but the difficulty of dealing with large number of in-sects and their unpredictability once released make significant bio-logical attacks with insects unlikely.

Diseases and deaths from contaminated water and food are alsowell known in nature. For example typhoid is transmitted by con-taminated water and botulism commonly comes from eatingimproperly canned food. One of most effective method for a biolog-ical attack is to dispense the bioagents as aerosol particles in theair, with depending on air movement to reach the target for largedistance. Bioagents then float in the air until they are inhaled. Aer-osol attack has following major advantages:

(1) The bio agents are dispersed in the air and driven by thewind can drift over large areas. During the sunny day,because of warm air lifts, disseminated aerosols may travelover a wide area but at kilometric altitude.

(2) Many diseases are more virulent when spread by the aerosolroute.

Description of biological agents

Lederberg and Primmerman [2,10] have discussed that bio-agents fall into five categories:

Bacterial agents, viral agents, rickettsiae, fungi and biologicaltoxins.

Bacterial-agents

Bacteria are small, single-celled organisms, most of which canbe grown on solid or liquid culture media. Diseases caused by bac-terial agents are Anthrax, Tularemia, cholera, Diphtheria, plagueand Typhoid fever.

Viral agents

Viruses are the simplest type of microorganisms. They consist ofprotein coat containing genetic material, either DNA or RNA.Viruses lack a system for their own metabolism; they require livinghosts (cells of an infected organism) for their replication. Diseasescaused by viral agents are Smallpox, Yellow fever, Dengue feverand Ebola.

Table 1Potential biological warfare agents.

Agents Type Disease Fatality

Bacillus anthracis Bacteria Anthrax HighYersinia pestis Bacteria Plague HighVariola major Virus Small pox HighClostridium botulinum Toxin Botulism HighFrancisella tularensis Bacteria Tularemia ModerateFilovirindea Virus Ebola High

Please cite this article in press as: D. Joshi et al., Detection of biological warfareActa Part A: Molecular and Biomolecular Spectroscopy (2013), http://dx.doi.or

Rickettsiae

Rickettsiae are obligate intracellular bacteria that are interme-diate in size between most bacteria and viruses and possess certaincharacteristics common to both bacteria and viruses. Diseasescaused by rickettsiae are – Q-fever, Endemic typhus and RockyMountain spotted fever.

Fungi

Fungi are unicellular or multi-cellular, microorganisms whichdo not contain chlorophyll. Most fungi do not cause fatal diseaseto humans but they can be used to destroy crops. In humans fungicause the disease Coccidioidomycosis.

Biological toxins

Biological toxins are poisons produced by living organisms. It isthe poison not the organism, which produces harmful effects in hu-man. Toxins of biological origin are- Botulinum Toxin, Saxitoxinand Ricin.

In this article we shall discuss about different types of biologicalagents. Detail of the potential bacterial, viral and rickettsiae biolog-ical agents is described by Fatah et al. [6] and given in the followingTables 2a–2c).

Among all types of bacterial biological agents listed, Bacillusanthracis is the weapon of choice for most of the terrorist groups[12]. Anthrax has the largest incubation period (The time differ-ence between something infected and appearance of first symp-tom) in comparison to other bacterial agents, which givesperpetrator a chance to escape. B. anthracis is highly lethal wheninhaled and enters the lungs. Thus B. anthracis has the propertiesthat make them attractive as potential biological warfare agent:

1. Retained potency during growth and processing to the endproduct (biological weapon).

2. Survival in atmosphere in aerosolized form (Long shelf life).

Anthrax is a disease caused by B. anthracis, which is a gram po-sitive, rod shaped bacterium, which has the ability of spore forma-tion. (Spore is the resting stage that enables the organism toendure adverse conditions, when conditions improve spore

Epidemic Lethal dose Vaccine Treat ability

No 10,000 cells Yes If detected earlyHigh 1000 Ineffective If detected earlyModerate 30 Yes NoNo 0.1 lg Yes NoNo 10–50 Ineffective YesModerate 3 No No



Table 2aDescription of bacterial type biological agents.

Biological agent/disease

Anthrax Brucellosis E. coli serotype Tularemia Cholera

Dissemination method 1. Spores in aerosol 1. Aerosol Water and food supplycontamination

1. Aerosol 1. Sabotage (food, water)

2. Sabotage (food) 2. Sabotage (food) 2. Rabbits or ticks 2. AerosolTransmissible person

to personNo (except cutaneous) Unknown Unknown, evidence

passed person-toperson in nursinghomes

No Rare

Incubation period 1–43 d Continued: Unknown 2–10 d 3–5 dDuration of illness 3–5 d (usually fatal) Unknown 5–10 d (most cases) >2 week >1 weekLethality Cutaneous anthrax: fatality

rate 5–20% Inhalationalanthrax: after symptomsappear almost always fatal.

Low 15% If develophemolytic uremicsyndrome (HUS); 5% ifdevelopthrombocytopenicpurpura (TTP)

Moderate if leftuntreated

Low (<1%) with treatment; high(>50%) without

Vaccine efficacy Currently no human data Vaccine underevaluation

No vaccine No commerciallyavailable vaccine

No data on aerosol

Symptoms and effects Flu-like, upper respiratorydistress; fever and shock in3–5 d, followed by death

Irregular prolongedfever, profuse sweating,chills, joint and musclepain, persistent fatigue

Gastrointestinal(diarrhea, vomiting)dehydration; in severecases, cardiac arrestand death, HUS, or TTP

Chills; sustainedfever; cough;prostration; tendencyfor pneumonia;enlarged, painfullymph nodes;

Sudden onset with nausea,vomiting, diarrhea, rapiddehydration, toxemia andcollapse

Potential as biologicalagent

High, Iraqi and USSRbiological programs workedto develop anthrax as a bio-weapon

Unknown Unknown High, if delivered viaaerosol form (highlyinfectious, 90–100%)

Not appropriate for aerosoldelivery


Diphtheria Glanders Melioidosis Plague (Bubonic andPneumonic)

Typhoid fever

Likely method ofdissemination

Unknown 1. Aerosol 1. Food 1. Infected fleas(Bubonic andPneumonic)

1 Contact with infected person

2. Cutaneous 2. Inhalation 2. Aerosol(Pneumonic)

2. Contact with contaminatedsubstances

3. Insect bites4 Contact withinfected animals

Transmissible personto person

High High No High(Pneumonic) High

Incubation period 2–5 d 3–5 d 1–2 d 1–3 d 7–14 dDuration of illness Unknown Unknown 4–20 d 1–6 d (usually fatal) UnknownLethality 5–10% Fatality 50–70% Variable 5–10% If Treated.

(Bubonic: 30–75%.Pneumonic: 95%) ifuntreated

<1% If treated; 10–14% ifuntreated

Vaccine efficacy (foraerosol exposure)/antitoxin

DPT vaccine 85% effective;booster recommended every10 yr

No vaccine No vaccine Vaccine not available Oral vaccine (Vivotif) and singledose injectable vaccine(capsular polysaccharideantigen); both vaccines offer65–75% protection.

Symptoms and effects Local infection usually inrespiratory passages; delayin treatment can causedamage to heart, kidneys,and central nervous system

Skin lesions, ulcers inskin, mucousmembranes, andviscera; if inhaled,upper respiratory tractinvolvement

Cough, fever, chills,muscle/joint pain,nausea, and vomiting;progressing to death

Enlarged lymphnodes in groin;septicemic (spleen,lungs, meningesaffected)

Prolonged fever, lymph tissueinvolvement; ulceration ofintestines; enlargement ofspleen; rose-colored spots onskin; constipation or diarrhea

Treatment Antitoxin extremelyeffective; antibiotic(penicillin) shortens theduration of illness

Drug therapy(streptomycin&sulfadiazine) iseffective

Antibiotics(doxycycline,chlorothenicol,tetracycline)

Doxycycline (100 mg2�/d for 7d);ciprofloxicin alsoeffective

Antibiotics (amoxicillin orcotrimoxazole) shorten andcure disease rapidly


transforms into active bacteria. In the spore stage B. anthracis cansurvive for decades and perhaps much longer).

In nature, anthrax most commonly occurs in cattle, sheep, goatsand horses, but can also infect humans. Anthrax may be spread bydifferent routes. Based on route of infection, anthrax is of threetypes – Inhalation, cutaneous and intestine.

1. Inhalation anthrax – Bacteria enter the body throughinhalation.


2. Cutaneous anthrax – Bacteria enter through cut on the skin.3. Intestine anthrax – This is caused by consumption of contami-

nated meat.

Intentional aerosol dissemination of spores represents the mostserious threat of all, as the spores are very stable and humanpopulation is susceptible to this form. The US Centers for DiseaseControl and Prevention Considers B. anthracis a category-A bioter-rorism agent.



Table 2bDepiction of viral category biological agents.

Biological agent/disease Marburg virus Junin virus Rift valley fever virus smallpox Smallpox Venezuelan equineencephalitis


Aerosol Epidemiology not known Mosquito-borne; in biologicalscenario, aerosols or droplets

Aerosol 1. Aerosol

2. Infected vectorsTransmissible person to

personUnknown Unknown Unknown High No

Incubation period 5–7 d 7–16 d 2–5 d 10–12 d 1–6 dDuration of illness Unknown 16 d 2–5 d 4 week Days to weeksLethality 25% 18% <1% 20–40% (Variola major) <1% Variola minor 1–60%Vaccine efficacy (for

aerosol exposure)/antitoxin

No vaccine No vaccine Inactivated vaccine available inlimited quantities

Vaccine protects against infection within 3–5 d of exposure

Experimental only:TC�83 protectsagainst 30 LD50s to500 LD50s inhamsters

Symptoms and effects Sudden onset of fever, malaise, muscle pain,headache, and conjunctivitis, followed by sore throat,vomiting, diarrhea, rash, and both internal andexternal bleeding (begins 5th day). Liver functionmay be abnormal and platelet function may beimpaired.

Hemorrhagic syndrome,chills, sweating,exhaustion and stupor

Febrile illness, sometimesabdominal tenderness; rarelyshock, ocular problems

Sudden onset of fever, headache, backache,vomiting, marked prostration, anddelirium; small blisters form crusts whichfall off 10–40 d after first lesions appear;opportunistic infection

Sudden illness withmalaise, spikingfevers, rigors, severeheadache,photophobia, andmyalgias

Biological agent/disease Yellow fever virus Dengue fever virus Ebola virus Congo-Crimean hemorrhagic fever virusLikely method of

disseminationMosquito-borne Mosquito-borne 1. Direct contact Unknown-

2. Aerosol (BA)Transmissible person to

personNo No Moderate Yes

Incubation period 3–6 d 3–15 d 4–16 d 7–12 dDuration of illness 2 week 1 week Death between 7 and 16 d 9–12 dLethality 10–20% Death in severe cases or full recovery after

2–3 d5% Average case fatality byproducing shock andhemorrhage, leading todeath

High for Zaire strain; moderatewith Sudan

15–20%


Vaccine available; confers immunity for >10 yr Vaccine available No vaccine No vaccine available; prophylactic ribavirinmay be effective

Symptoms and Effects Sudden onset of chills, fever, prostration, aches,muscular pain, congestion, severe gastrointestinaldisturbances, liver damage and jaundice;hemorrhage from skin and gums

Sudden onset of fever,chills, intense headache,pain behind eyes, joint andmuscle pain, exhaustionand prostration

Mild febrile illness, thenvomiting, diarrhea, rash, kidneyand liver failure, internal andexternal hemorrhage (begins 5thday), and petechiae

Fever, easy bleeding, petechiae,hypotension and shock; flushing of face andchest, edema, vomiting, diarrhea

Treatment No specific treatment; supportive treatment (bedrest and fluids) for even the mildest cases

No specific therapy;supportive therapyessential

No specific therapy; supportivetherapy essential

No specific treatment


High, if efficient dissemination device is employed Unknown Former Soviet Union Unknown

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Table 2cDescription of rickettsiae type biological agents.


Endemic typhus Epidemic typhus Q fever Rocky mountain spotted fever


1. Contaminated feces 1. Contaminated feces 1. Sabotage (food supply) Infected wood ticks

2. Infected insect larvae 2. Infected insect larvae 2. Aerosol3. Rat or flea bites

Transmissible personto person

No No Rare No

Incubation period 6–14 d 6–15 d 14–26 d 3–14 dLethality 1%, Increasing in people > 50 yr old 10–40% Untreated; increases

with ageVery low 15–20% Untreated (higher in

adults); treated—death rarewith specific therapy(tetracycline orchloramphenicol)


Unknown Vaccine confers protection ofuncertain duration

94% Protection against 3500LD50s in guinea pigs

No vaccine

Symptoms and effects Sudden onset of headache, chills,prostration, fever, pain; maculaeeruption on 5–6th d on upper body,spreading to all but palms, soles, orface, but milder than epidemic form

Chills, sudden onset of headache,prostration, fever, pain; maculaeeruption on 5–6th d on upperbody, spreading to all but palms,soles, or face

Mild symptoms (chills,headaches, fever, chestpains, perspiration, loss ofappetite)

Fever and joint pain, muscularpain; skin rash that spreadsrapidly from ankles and wriststo legs, arms, and chest;aversion to light

Treatment Antibiotics (tetracycline andchloramphenicol); supportivetreatment and prevention of secondaryinfections

Antibiotics (tetracycline andchloramphenicol); supportivetreatment & prevention ofsecondary infections

Tetracycline (500 mg/6 h, 5–7 d) or doxycycline (100 mg/12 h, 5–7 d) also,Erthyromycin (500 mg/6 h)&rifampin (600 mg/d)

Antibiotics—tetracycline orchloramphenicol


Uncertain––broad range of incubation(6–14 d) period causes infection offorce deploying biological agent.

Uncertain––broad range ofincubation (6–14 d) period couldcause infection of forcedeploying biological agent.

Highly infectious, isdelivered in aerosol form.Dried agent is very stable;stable in aerosol form.

Unknown

Table 3Simulants of important biological agents.

Biological warfare-agent Its simulant Characteristics of thesimulant

Bacillus anthracis Bacillus cereus Vegetative Bacillus cells: G-pos rod

Bacillus anthracis Bacillus subtillis Veg Bac. cells: G-pos rodBacillus anthracis Bacillus globigii

sporesBacterial spores

Bacillus thuringiengis Insecticide/interferent

Veg Bac. cells: G-pos rod

Yersinia pestis/plague Yersinia Rohdei Veg Bac. cells: G-neg rodYersinia pestis stimulant/

plagueErvinia herbicola Vegetative bacterial cells

Biological-toxin Ova albumin ProteinBiological-toxin Albumin, bovine

serumProtein


Virulence factors of B. anthracisThe lethality of anthrax bacterium B. anthracis is due to two vir-

ulent factors: its anti-phagocytic polysaccharide capsule (whichprevents the cells of the immune system from killing the bacteria)and its secretion of the anthrax toxin (which is cytotoxic tomacro-phases primarily) [13,14]. The toxin is a mixture of three proteins:protective antigen (PA), edema factor (EF), and lethal factor (LF).The two virulent enzymes, EF and LF, depend on PA, which actsas a Trojan horse to carry them through the plasma membrane intothe cell where they can make their attack. The three proteins of the

Table 4Peak excitation and fluorescence wavelengths of bacterial-fluorophores.

Compound Excitation (nm) Emission (nm) Lifetime (ns)

Tryptophan 280 340 0.79(12%), 3.06Tyrosine 275 304 3.6Phenylalanine 260 282 6.8NADH 346 457 0.48Folic acid 361 442 1.60(12%), 4.78


anthrax toxin depend on each other for their toxic effect. Each pro-tein is nontoxic on its own, but when combined, these proteinsproduce the lethal symptoms of anthrax. When injected in labora-tory animals, the combination of EF and LF shows no effect. Thecombination of PA and EF, however, cause local edema, and PAmixed with LF rapidly leads to death. These studies show thatthese proteins work synergistically, where EF and LF depend onthe presence of PA for the toxic effect. To study about biologicalagents in lab environment their simulants are taken. Table 3 de-scribes about simulants of important biological agents [15].

Biological aerosol particles have an excitation in UV (ultravio-let) band of spectral region 250–380 nm and exhibit a fluorescencespectrum peaking extending over a wide range between 300 and600 nm depending on the type of bacteria. Table 4 shows peakexcitation and fluorescence wavelengths of bacterial-fluorophores[16].

The fluorescence spectrum of biological aerosols have beenattributed to the aromatic amino acids, specially tryptophan, andto a lesser extent tyrosine and phenylalanine, which are presentin cell material of all biological organisms and the cell wall of bac-terial endospores. To make distinction between cell of biologicalorganisms and bacterial endospores some specific signature of bac-terial endospores is required. Studies show that DPA dipicolinicacid (2,6-pyridinedicarboxylic acid, C7H5NO4) and its salts are ma-jor constituents of bacterial endospores and rather uncommonelsewhere in nature [5]. So spectroscopic detection of B. anthracisspores can be focused on the signatures from DPA [17,18]. Forspectroscopic study of B. anthracis in lab environment simulantsof B. anthracis are taken. Table 5 shows Peak excitation and fluores-cence wavelengths of simulant of B. anthracis [19].

The biomolecules such as aromatic amino acids, particularlytryptophan and tyrosine and nucleotides NADH involved in the cellmetabolism have strong absorption bands in the spectral regionranging from 280 to 380 nm and emitting in the 300–600 nm re-gion [20]. Fig. 2 shows the fluorescence intensity of biomoleculefor 266 nm excitation [21].



Table 5Peak excitation and fluorescence wavelengths of simulant of Bacillus anthracis.

Fluorescent species Fluorescence cross section(cm2/sr.nm.particle) Excitation wave length (nm) Fluorescence wavelength (nm) Particle size

BG vegetative 5 � 10�14 280 320 5–10 lmBG spores 5 � 10�15 280 310 1–2 lmBm 2 � 10�14 280 318 5–10 lmBG vegetative 3.5 � 10�15 266 320 Dry aerosolBG aerosol 1.6 � 10�14 266 310 Wet aerosolBm spores 3 � 10�14 280 318 Liquid suspension

Fig. 2. Fluorescence intensity of biomolecules for 266 nm excitation.


Criteria for detection techniques

Biological agents are effective in very low doses. Therefore, bio-logical agent detection systems need to exhibit high sensitivity(i.e., be able to detect very small amounts of biological agents).The complex and rapidly changing environmental background alsorequires these detection systems to exhibit a high degree of selec-tivity (i.e., be able to discriminate biological agents from otherharmless biological and non-biological material present in theenvironment). A third challenge that needs to be addressed isspeed or fast response. These combined requirements provide asignificant technical challenge. Since the effective way for thedelivery of bio-warfare agents is through airborne aerosol route,so techniques which give an early warning regarding the presenceof a biological aerosol cloud is required i.e. standoff/remote detec-tion techniques are required.

Standoff detection system has the sensor system at a distanceaway from the area of interest and Remote detection has thesensor system in vicinity of area of interest. (Remote sensing isthe stand-off collection through the use of variety of devicesfor gathering information on a given object or data. Remotesensing makes it possible to collect data on dangerous or inac-cessible areas). Stand-off detection of biological agents can bedone using LIDAR (light detection and ranging) technique. Thereare two basic requirements that should be fulfilled for a LIDARto work properly:

� The object to be examined must have a signature of some kindthat is different form the background and other objects.� This signature should be in a spectral band with good atmo-

spheric transmission.

The principles of operation for LIDAR are similar to those for ra-dar: a light pulse is transmitted and signal scattered along its trav-eling part is recorded as a function of time. Range gated is aspecialized LIDAR technique where detection electronics is turnon for a specific interval of time.


In a fluorescence LIDAR, auto fluorescence excited by a UV laserfrom biological cells is utilized to classify the fluorescing biologicalcells from other non-biological or naturally occurring particles. La-ser Induced Fluorescence (LIF) is a technique based on the absorp-tion of laser light. Atoms that absorb laser light go into excitedelectronic states and eventually return to the ground electronicstate via radiative frequency and detected in the longer wave-length band [22]. UV induced bio fluorescence is a potentially suc-cessful strategy because it involves no chemical consumables andit is an online detection method where particles can be interro-gated without impaction onto a substrate.

Fluorescence

Fluorescence is a special case of luminescence the emission oflight not solely related to the temperature of the luminous object.Absorption of incident radiation in a molecule leads to an elec-tronic transition within the molecule. The molecule can then relaxback to its original state (normally the ground state) through sev-eral processes. In some cases, this relaxation process includes theemission of a photon from singlet to singlet transitions, which isknown as fluorescence. Other relaxation processes, like vibrationaltransitions, intersystem crossing, or loss of energy through molec-ular collisions, do not include emission of photons (non-radiative).In the case of fluorescence, this often occurs in combination withnon-radiative processes, thus reducing the energy (i.e. frequency)of the emitted photon. This may lead to a spectrum of the fluores-cence that is characteristic for a particular molecule. The decaytime of fluorescence is typically in the range from nanosecondsto micro-seconds [22,23]. Not all molecules will emit fluorescence,and for those who do, the fluorescence often depends strongly onthe excitation frequency, as there may be certain molecular transi-tions that, when excited, give rise to fluorescence.

Fluorophores

Most of the bioagents, like the B. anthracis (anthrax), are bacte-ria of typically 1.0 lm in size [24,25]. Depending on the dissemina-tion conditions, they can agglomerate in clusters of sizes up to10 lm. They contain natural fluorophores, like amino acids (e.g.tryptophan), nicotine amides (NADH), and flavins (e.g. riboflavin(RBF) and flavoproteins), which can be used as characteristic trac-ers of their biological nature. In the context of standoff detection ofbiological aerosols, two molecules are of particular interest; NADHand tryptophan. NADH is the reduced form of nicotinamide ade-nine dinucleotide (NAD+), and is important in cell respirationand hence metabolism. NADH is therefore present in bacteriaand other living cells, but to a lesser degree in spores or viruses.Tryptophan is an amino acid, and thus present in all biologicalmaterial, including viruses. Also other biological molecules emitfluorescence, but to a lesser degree, and less relevant for standoffdetection. Native fluorescence detection and spectral differentia-tion of peptides containing tryptophan and tyrosine in capillaryelectrophoresis has been studied [26].



Fig. 3. Absorption spectra of the three fluorescing amino acids, tryptophan, tyrosineand phenylalanine.

Fig. 4. Emission spectrum for tryptophan and tyrosine excited at 266 nm.


Tryptophan

Tryptophan is an amino acid, i.e. one of the building blocks inthe protein synthesis that occur in cells. Tryptophan has absorptionpeaks at 230 nm and 280 nm, the latter being of particular interestin standoff detection applications. When excited at 280 nm, trypto-phan emits fluorescence with a peak around 350 nm. Tryptophancan also be excited at other UV wavelengths, but with reducedfluorescence intensity as a possible result. For example, excitationwith the common laser wavelength at 266 nm would result inabout 25% of the fluorescence when excited at 280 nm. In Fig. 3,the absorption spectra of the three fluorescing amino acids, trypto-phan, tyrosine and phenylalanine, are shown. In Fig. 4, the emis-sion spectrum for tryptophan is shown after excitation with266 nm.

Other fluorescent molecules

There are two other molecules that may be relevant for UV laserinduced fluorescence; flavins and dipicolinic acid (DPA). The sourceof flavins is the vitamin riboflavin. The peak absorption wavelengthis �450 nm, and the emission peak is at �550 nm. DPA is formedduring spore formation and shows absorption peak in the wave-length region between 340 and 360 nm.

Principle of UV-LIF LIDAR system

The most widely studied standoff bio-signature is UV Laser-In-duced Fluorescence (LIF) [27]. The principle standoff fluorescencesignature will be dominated by NADH spectra when excited using


UV wavelengths in the 300–360-nm range and will be dominatedby Tryptophan when excited with 260–280 nm wavelength band.Lifetime is on the order of 12 ns; thus it can be range-resolved withthe backscatter signal [28]. Atmospheric transmission is a majorconcern in choosing the excitation wavelength for a standoff UV-LIF detection system because of increased Rayleigh scatteringlosses while moving towards UV wavelength band. A commonlytransmitted wavelength is the third harmonic of Nd:YAG(355 nm), since Nd:YAG is a highly reliable solid state laser source.Other sources have been suggested as providing a higher signal[29]. Some systems have opted to use shorter wavelengths (suchas the fourth harmonic of Nd:YAG, 266 nm), which excite addi-tional flurophores (such as tryptophan), but this further limitsthe range sensitivity of the system due to more increase Rayleighscattering losses.

Experimentally the range-resolved detection and identifica-tion of biological aerosols in the air by non-linear LIDAR has alsobeen demonstrated. Ultra-short terawatt laser pulses are used toinduce two-photon-excited fluorescence (2PEF) in riboflavin con-taining particles at a remote location. It is shown that, in thecase of amino acid detection, 2PEF-LIDAR should be more effi-cient than linear 1PEF-LIDAR beyond a typical distance of2 km, because it takes advantage of the higher atmospherictransmission at the excitation wavelengths [30]. Ultra short laserpulses from the Teramobile were used to induce in situ two-photon excited fluorescence (2PEF) in the aerosol particles[31,32].

Operation of the UV LIDAR

Fig. 5 Demonstrates typical experimental set-up for operation ofthe UV-LIDAR for biological agents detection [33,34].

The Nd: YAG laser output is directed towards an airborne bio-logical cloud. Fundamental (1.06 micron) wavelength can be usedfor depolarization measurements. Using second harmonic(532 nm) or third harmonic (355 nm) range and width of cloudcan be detected by Photomultiplier Tube (PMT). For the fluores-cence measurements third and fourth harmonics wavelength areused. Laser light is scattered backwards elastically via Mie scatter-ing, while part of it is absorbed by biological cloud that subse-quently emit light at lower frequencies than the excitation (laser)frequency (inelastic scattering, or fluorescence). A small amountof the scattered light is collected by the telescope and spectrallyseparated by dichroic mirror such that the elastically scatteredlight impinges on a fast detector (photomultiplier tube or APDfor depolarization), whereas the lower-frequency light (fluores-cence signal) is directed into a spectrograph and detected by agated Intensified Charge Coupled Device (ICCD) camera/Multi-An-ode Photo Multiplier Tube (MAPMT). The PMT measures the timeof flight of laser pulse, thereby measure the distance and depthof the cloud of interest. These parameters are used to control thegating and delay time of ICCD and MAPMT detectors, in order tocollect light from the range of interest. ICCD detector combinesan image intensifier and a Charge Coupled Device (CCD) cameravia fiber coupling. An image intensifier typically consists of threecomponents, a photocathode, a Micro-Channel Plate (MCP) and aphosphor screen. The ICCD detector can be gated unlike CCD detec-tor hence provides more sensitivity of measurements. Also CCD hasa gain of 1 while ICCD detectors have gain of 103 [35]. The MAPMTis composed of a cathode, a dynode chain and a segmented anode.Its structure is optimized to ensure the spatial distribution of pho-tons incident upon the cathode to be reproduced faithfully as thesignal at the anode. Similar to the conventional PMT, the MAPMThas a quantum efficiency (>15% in the blue/green spectral range),negligible read-out noise, and minimal dark noise with cooling



Fig. 5. UV-LIF LIDAR Schematics.


MAPMT have a typical gain of 106 much greater than ICCD detectorhaving gain of 103 only. MAPMT has more data transfer rate ascompare to ICCD detector [36].

A methodology for depolarization measurement to classify theaerosol biological cloud or chemical cloud is also depicted inFig. 5 having Glan-Thomson (GT) polarizer and two detectors(APD1 and APD2) for measurement of s and p-polarization sepa-rately. The depolarization ratio nearly one shows presence ofchemical species in cloud due to spherical shape of chemical vapor.Depolarization ratio less than or greater than one indicates ellipti-cal shape particles in aerosols which may be attributed to bacterialagents inside the cloud [37,38].

Theoretical analysis

This section deals with the theoretical calculation of stand-offfluorescence return signal from a biological cloud. The fluorescencesignals are calculated for a cloud at a location of 2.0 km at variousconcentration of B. globigii. Theoretical studies and estimation areperformed using ICCD and MAPMT detector in presence of solarbackground. Eq. (1) is the key LIDAR equation in theoretical esti-mation of fluorescence signal from bio-aerosols cloud.

Evaluation of LIF LIDAR signal

The factors that influence the detection process in a LIDAR canbe described in LIDAR equation [39]. This is given below in Eq. (1),and describes the spectrally distributed inelastic scattering, by asingle type of inelastic scattered, collected by the instrument(before the detector).

Ef ¼ ET :TðRÞ:K0ðkÞ:nðRÞ:A

R2 :Nf :ðDRÞ: drf

dX

� �ð1Þ

PA

Ef

lease citecta Part A

Energy received
ET Energy transmitted = 100 mJ T (R) Atmospheric attenuation K0 (k) Receiver Transmission efficiency = 0.8
this article in press as: D. Joshi et al., Detection of biological warfare ag: Molecular and Biomolecular Spectroscopy (2013), http://dx.doi.org/1

n

ents usin0.1016/j

Overlap factor of receiver and transmitter = 1
A Aperture area = 0.0707 m2
R
Range: cloud distance Nf Number of fluorescence species DR Cloud depth = 50 m
ðdrf

dXÞ
Total differential cross section = 10�16 m2/bacteria-stredian
Moderate visibility of 10 km is taken to calculate the atmosphericattenuation.

T(R) = exp (�(a1 + a2).R) where a is average of attenuation coef-ficient for outgoing laser and received radiations.

a1 ðkm�1Þ ¼ 3:91V� 0:550

k1

� �0:585:V1=3

and a2 ðkm�1Þ

¼ 3:91V� 0:550

k2

� �0:585:V1=3

ð2Þ

V is the visibility (km) and a1 and a2 are the attenuationcoefficient for k1 (Laser wavelength) and k2 (Fluorescence returnwavelength).

The SNR (expressed as a current ratio rather than electricalpower ratio) calculated for parameters at the photocathode is ex-pressed as

SNRMAPMT ¼is

inð3Þ

is and in are the signal and noise current respectively.Noise current is given by the expression

in ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðis þ ib þ idÞ

et

r; ð4Þ

is, ib, and in are the signal, background and noise currentrespectively.

Each of the 32 channels will have individual values of is, ib, andin and so the SNR. Fig. 6 depicts the parameters involved in calcu-lation of fluorescence received energy.

g ultra violet-laser induced fluorescence LIDAR, Spectrochimica.saa.2013.04.082


Theoretical Estimation of Fluorescence signal from bio-aerosols cloud

Aperture

Transmitted Energy

Received Energy

R1 R2

Solar Background

Bio aerosols Cloud

Kσ f , N

Detector ParametersLaser Energy and Wavelength

Receiver parameters

Solar backgroundAtmospheric attenuation

Range of CloudCloud depth and Concentration

Fluorescence molecule

Fig. 6. Theoretical estimation of parameters of fluorescence signal from Bio-aerosol cloud.


Parameters of UV-LIF LIDAR system

PA

Lasers

lease cite this article in pcta Part A: Molecular and

266 nm Nd: YAG Laser
Laser energy 100 mJ@266 nm PRF 10 Hz Pulse width �6 ns Target location Up to 5 km. Peak emission
wavelength:
350 nm (typical to tryptophanfluorescence signature)
Fluorescence cross section of bacteria = 10�16 m2/stredian/particle (typical value)

Receiver type
Newtonian telescope Receiver diameter 30 cm Field of view 0.83 milli-radian Grating efficiency 50% Detector Gated ICCD/MAPMT
Operation parameters
Sky background 0.0001–0.1 W/m2 nm for 300–500 nm
band
Atmospheric
visibility
10 km (moderate)
Bio-aerosols
Bacillus globigii Concentration 104–106 bacteria/L of air (106 is �1 ppb
concentration)

Solar background contribution

The challenge in UV-LIF based biological sensor is that the fluo-rescence band and the Solar spectra are overlapping with eachother [40–44]. Total power received at the top of the earth’s atmo-sphere from the Sun is 1366 W/m2 (radiant flux). Corresponding toan Albedo of 0.7 the radiant flux on earth surface is �960 W/m2.Spectral irradiance is the irradiance at a given wavelength per unitwavelength interval [44]. In the case of our system the diffuse irra-diance is important as the sensor is looking towards the sky notany topographic target. The 5 min averaged value diffuse irradi-ance, centered at 1120 h is 267 W/m2 [44]. Average Diffuse spectralirradiance value is taken 0.1 watt/m2 nm for 300–500 nm band.During the twilight condition (onset of day and night) the solarirradiance is �1/1000 of its value in daytime. Therefore for twilightaverage diffuse spectral irradiance value is taken 0.0001 W/m2 nmfor 300–500 nm band.

ress as: D. Joshi et al., Detection of biological warfareBiomolecular Spectroscopy (2013), http://dx.doi.or

Received fluorescence photons vs. range in presence of solarbackground photons at different particle concentration were de-rived from LIDAR Eq. (1). For the above LIDAR parameters the solarbackground photons corresponding to an integration time 333 ns,FOV of system 0.83 milliradian and a spectral bandwidth of100 nm corresponds to 1.8 � 105 photons as received by the opti-cal receiver/telescope. It can be seen that daylight will have a se-vere impact on the threshold resolution due to shot noisegenerated in the detector.

Gated MAPMT is able to record the fluorescence spectra from adistance of 3.9 km in daytime and 5.5 km at twilight condition for106 (�order of 1 ppb) bacteria/L concentrations for averaging timeof 1.0 min (corresponding to 600 pulses). For a comparison at the2.0-km range, the minimum detectable concentration during day-time for gated ICCD is 2 � 106 bacteria/L for averaging of 600pulses. For gated MAPMT under the same condition minimumdetectable concentration is 104 bacteria/L.

International scenario

Internationally, a large amount of defense research is currentlybeing conducted to develop LIDAR technology to provide remotedetection of a biological agent attack. The US DoD funded Joint Bio-logical Standoff Detection System (JBSDS) is close to being fielded.JBSDS excites LIF in biological and fluorescent interferent materialusing a 355 nm laser. It performs cloud mapping and particle sizingwith an IR laser and uses an algorithm to compare the magnitudeof a single fluorescence band and elastically scattered IR returns todiscriminate a biological release from interferent material. It is rel-atively small and can be installed on the back of a military vehiclerequiring generator power. The Canadian Standoff Integrated Bio-aerosol Active Hyperspectral Detection (SINBAHD) system uses ahigh energy (150–200 mJ 351 nm excimer laser to induce fluores-cence and collects high resolution spectra from aerosols. It uses atrained algorithm to discriminate biological materials using thesespectra, normalized to the atmospheric nitrogen Raman return.The system is a prototype housed in a 12 m trailer; however, ithas the potential to be a much smaller system. The Norwegian sys-tem also measures high resolution spectra from biological mate-rial, exciting fluorescence with a pulsed 355 nm (frequencytripled) Nd: YAG laser. In contrast, the UK system is investigatingthe discrimination capability of a spectrally resolving LIF LIDARusing pulsed 266 nm radiation from a frequency quadrupledNd:YAG laser, using 10 broad spectral bands to collect low resolu-tion spectra. The latest development of this system utilizes the




elastic backscatter from 1064 nm IR radiation provided by theresidual fundamental Nd: YAG laser to detect and map clouds.The system is relatively small and is housed in a 5 m trailer. Otherresearch systems are also being developed within Europe, forexample, the German CBRN center is evaluating a multiple wave-length LIDAR using 1064 nm IR elastic scatter, 532 nm for depolar-ization measurements and 266/355 nm to induce fluorescencefrom clouds. A consortium of European companies and researchagencies are demonstrating a novel 280 nm and 355 nm basedLIF LIDAR for shorter range civil applications under the BiologicalOptical Defense Experiment (BODE) for Preparatory Action forSecurity Research (PASR).

Conclusion

Biological agents have features that an adversary may findattractive as an agent of war or terrorism. B. anthracis bacteriaare identified as the first weapon of choice due to its property offorming spores in adverse condition. To protect potential victimsfrom infection and harm, rapid and accurate detection and identi-fication of bioagents is required. The principal approach to earlywarning sensing today is laser-induced fluorescence LIDAR, takingadvantage of ubiquitous biological constituents that emit light inresponse to excitation in the UV (particularly tryptophan andNADH). Using UV-LIF LIDAR biological and non-biological signaturecan be distinguished by separating plane polarized s and p compo-nents of the received Mie scattered signal. If biological sample ispresent then total fluorescence is collected on the PMT and disper-sive fluorescence signal information collected using ICCD spec-trometer/MAPMT. We conclude that in terms of sensitivity andrange, MAPMT based system offers better performance as com-pared to ICCD based system. Advances in hybrid PMT with multiplechannels in the future may result in a better sensor for this type ofapplication. Range and sensitivity of the system can be improvedby using ultra-short terawatt laser pulses to induce two-photon-excited fluorescence (2PEF). This review presents the moderninternationally available UV-LIF LIDAR systems. UV-LIF LIDAR sys-tem is considered as the best system for standoff detection of bio-logical aerosols till date.

Acknowledgement

Authors wish to thank Professor S.N. Thakur, Banaras HinduUniversity for fruitful Discussions.

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