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Sensors and Actuators B 147 (2010) 191–197
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical
journa l homepage: www.e lsev ier .com/ locate /snb
oly[meso-tetrakis(2-thienyl)porphyrin] for the sensitive electrochemicaletection of explosives
ei Chena, Ying Wanga, Christian Brücknerb, Chang Ming Li c, Yu Leia,∗
Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, 191 Auditorium Rd, Storrs, CT 06269, USADepartment of Chemistry, University of Connecticut, Storrs, CT 06269, USASchool of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637457, Singapore
r t i c l e i n f o
rticle history:eceived 7 November 2009eceived in revised form 11 March 2010ccepted 12 March 2010vailable online 17 March 2010
a b s t r a c t
Poly[meso-tetrakis(2-thienyl)porphyrin] (pTTP) was prepared through electrochemical polymerizationof meso-tetrakis(2-thienyl)porphyrin (TTP). The pTTP film thus generated was characterized by cyclicvoltammetry (CV), SEM, and Raman spectroscopy. The ability of the pTTP-modified electrode for thedetection of a range of explosives in aqueous solution was investigated using differential pulse voltam-metry (DPV). The results demonstrate that pTTP film greatly enhances the reduction of 2,4-DNT, TNT,
eywords:TTPifferential pulse voltammetryxplosive detectionitroalkaneitroaromatic compound
Tetryl, RDX, and nitromethane when compared to an unmodified electrode, a TTP-modified electrode,or a polythiophene-modified electrode. This may be attributed to the high affinity of the porphyrin ringin the pTTP conducting chain to the nitrocompound and the resulting enhanced electron transfer dur-ing the explosives reduction. Under optimized conditions, the pTTP-modified electrode shows a limit ofdetection (S/N = 3) as low as 8 ppb for 2,4-DNT and TNT, 9 ppb of Tetryl, 96 ppb of RDX, and 43 ppb ofnitromethane without requiring any sample pre-concentration step. This study indicates that pTTP canserve as a new class of material in the electrochemical detection of explosives.
. Introduction
2,4-Dinitrotoluene (2,4-DNT), 2,4,6-trinitrotoluene (TNT),yclotrimethylenetrinitramine (RDX), and trinitrophenyl-N-ethylnitramine (Tetryl) are today the most commonly used
xplosives (Scheme 1 ) [1]. Their production and wide militarynd civil uses have lead to severe contamination of the waterystem [2]. All the explosives are known toxins to humans [3]. Thisircumstance alone demands their efficient detection in aqueousnvironment, and this public health challenge has received consid-rable attention [4]. In addition, terrorism has emerged as a threato public safety throughout the world. The most common formf terrorism uses conventional explosives and has cost the livesf far more people than biological, chemical or radioactive threatubstances combined have claimed, though the latter are generallyn the forefront of the public mind. The extension of terrorismctivities from land to marine environments has also elevated the
riority of the detection of explosives in aqueous environment5,6]. Nitromethane has also been used in the preparation ofome-made explosives. This liquid is readily acquired as it is useds a fuel or fuel-additive in certain motor sports. Nitromethane∗ Corresponding author.E-mail address: [email protected] (Y. Lei).
925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.snb.2010.03.046
© 2010 Elsevier B.V. All rights reserved.
is in fact a more energetic high explosive than TNT, although thelatter is characterized by a higher velocity of detonation and higherbrisance. Thus, the detection of nitromethane is also extremelyimportant.
In the past decades, a number of technologies were developedfor the detection of explosives in aqueous samples. The approvedstandard technology for trace explosive detection is the US EPAprotocol SW-846 Method 8330 involving reverse-phase HPLCwith UV detection [7]. Others reported methods include chemi-luminescence [8,9], spectrophotometric assays [10,11], the use ofimmunosensors [12–16], and surface enhanced Raman scattering[17]. However, electrochemical methods, owing to their rela-tively low cost, efficiency, high sensitivity, and ease of operation,have emerged as preferable for the detection of commercial andhome-made explosives [1,5,18]. Various electrochemical methods,such as anodic stripping voltammetry, square wave voltamme-try, cyclic voltammetry, and amperometry, have been extensivelyexplored in the detection of explosives [1,3,6,18–24]. In addition, arange of electrode materials, such as carbon nanotubes [18], car-bon nanotube-metallic nanoparticle composites [25], core-shell
tin–carbon [26], and boron doped diamond [20], have been usedto enhance the electrochemical reduction wave, thereby increasingthe sensitivity of the electrochemical detection of explosives. Eventhough many of these systems and materials are functional or evenelegant, many do not lend themselves to large scale production, are
192 W. Chen et al. / Sensors and Actua
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and reduction currents increase regularly, indicative of the growthof a conducting pTTP layer. The anodic peak at ca. +0.73 V can beassigned to the oxidation of the porphyrin ring [38], while the con-
Scheme 1. Chemical structures of analytes.
ostly, have short lifetimes, or have other practical disadvantages.herefore, new and improved materials and methods for explosivesensing are still in great demand.
Porphyrins are tetrapyrrolic, aromatic macrocycles. The mostharacteristic property of porphyrins is their large aromatic �-ystems that are at the origin of their deep coloration, theiristinctive electronic spectra, and their photo- and electrochem-
cal activity. A wide range of naturally occurring and syntheticorphyrins are available. Porphyrins and their metal complexesmetalloporphyrins) have attracted considerable attention aslectrocatalyst for reduction and oxidation processes [27–31].lectron-deficient analytes, such as nitroaromatic compounds,ave a natural affinity to electron-rich porphyrins. This interac-ion perturbs the porphyrin �-system. This, in turn, is reflected inheir altered electronic properties. Thus, the porphyrin-explosivesnteraction has become the basis for the fluorescence detectionf nitroaromatic explosives [32–35]. To incorporate the explo-ives affinity of porphyrins and their electrocatalytic propertyithin polythiophene, we envisioned that the known thiophene-erivatized porphyrin meso-tetrakis(2-thienyl)porphyrin (TTP) cane polymerized to provide a conducting polymer that incorporatesorphyrin moieties in its conductive chains [36]. We will reportere that, indeed, TTP can be electropolymerized as a film onto anlectrode, and that the resulting polymer film-modified electrodexhibits enhanced electrocatalytic properties when compared toolythiophene-coated, TTP-coated, or untreated electrodes. Theoating can be exploited for the sensitive detection of explosivesn aqueous solution using differential pulse voltammetry (DPV).
. Materials and methods
.1. Chemicals
meso-Tetrakis(2-thienyl)porphyrin (TTP) was synthesized usingnown procedures [36,37]. Tetrabutylammonium hexafluorophos-hate (TBAPF6), thiophene, DNT, and nitromethane were purchasedrom Aldrich, dichloromethane (CH2Cl2) and sodium phosphate
onobasic monohydrate (NaH2PO4·H2O) from Acros, and anhy-rous dibasic sodium phosphate (Na2HPO4) from Fisher Scientific.he standard solutions of TNT, Tetryl, and RDX in acetonitrile (all000 �g/mL) were purchased from Supelco (Bellefonte, PA), Ultra
cientific (North Kingstown, RI), and Chem Service (Westchester,A), respectively. Conductive ITO glass slides (50–100 �/sq) werebtained from Nanocs (New York, NY). Dichloromethane was useds solvent with TBAPF6 as supporting electrolyte for the electro-tors B 147 (2010) 191–197
chemical polymerization of TTP onto glassy carbon (GC) electrodes(dia. 3 mm).
2.2. Apparatus
The cyclic voltammetric (CV) deposition of pTTP and differ-ential pulse voltammetric measurements were performed usingan electrochemical workstation (Bio-logic VMP3) with a conven-tional three-electrode configuration, including a working electrode(bare or modified GC electrode), an Ag/AgCl reference electrode,and a platinum counter electrode. Before each experiment, thesolution was purged with compressed nitrogen for 15 min. Themorphology of the electropolymerized pTTP film was character-ized using JEOL 6335F Field Emission Scanning Electron Microscope(FESEM). The Raman spectra were recorded on a Renishaw Ramas-cope Micro-Raman with 512 nm wavelength laser to investigate thebond stretching of the as-prepared pTTP film and the TTP monomer.
2.3. Electrochemical deposition of pTTP
All electrochemical experiments were carried out in an electro-chemical cell with a working volume of 5 mL at room temperature.Before electrochemical polymerization of TTP, the GC electrodewas polished sequentially with fine-grade alumina powders (1, 0.3,and 0.05 �m) to obtain a smooth and shining surface. The elec-trochemical deposition of pTTP films was carried out by cyclicvoltammetry (0–2.0 V at 20 mV/s). The electrolyte consisted of1 mM TTP monomer and 0.1 M TBAPF6 in CH2Cl2. After the elec-tropolymerization, the pTTP-coated GC electrode was washed withCH2Cl2 to remove any non-polymerized TTP. For SEM and Ramaninvestigation, pTTP films were deposited on a small piece of con-ductive ITO glass under the same conditions.
2.4. Electrochemical detection of explosive compounds
The detection of explosives (2,4-DNT, TNT, Tetryl, RDX, andnitromethane) was performed by differential pulse voltammetryin 0.01 M pH 7.0 phosphate buffer solution. Prior to the measure-ments, the solution was purged with compressed high purity N2 for15 min, and a gentle N2 stream was maintained over the solutionduring the measurements. The differential pulse voltammetry wasrecorded using the optimized DPV parameters, 50 mV pulse height,250 ms pulse width, 5 mV step height, and 500 ms step time.
3. Results and discussion
3.1. Electrochemical synthesis of pTTP
Repetitive cyclic voltammetry scans of a TTP monomer (1 mM)and TBAPF6 (0.1 M) in CH2Cl2 solution provide clear indicationsfor an electrochemical polymerization and growths of a pTTP con-ducting film on the GC electrode. In the first two cycles (Fig. 1,inset), there are three anodic peaks. Their origin is not clear atcurrent stage, but tentatively attributed to the oxidation of theporphyrin, the meso-2-thienyl groups, and/or the trace amounts ofimpurities present in the meso-tetrakis(2-thienyl)porphyrin. Afterthe first four cycles, the electrode is stabilized and the oxidation
tinuous increase of the oxidation current above +1.2 V with theincrease of scanning cycles can be attributed to the successive oxi-dation of meso-2-thienyl groups and the deposition of conductingpTTP film on the GC electrode.
W. Chen et al. / Sensors and Actuators B 147 (2010) 191–197 193
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ig. 1. Cyclic voltammogram of the pTTP film growth (after the first four cycles).he inset shows the first four CV cycles. Electrolyte: 1 mM TTP and 0.1 M TBAPF6 inH2Cl2. Scan rate = 20 mV/s.
.2. Raman and SEM characterizations of the pTTP film
Scheme 2 shows the proposed constitution of the pTTP film.ote that in TTP, one �-position in each of the four thiopheneser TTP is unsubstituted. Based on the known reactivity of thio-hene and the constitution of polythiophene, this position is theost likely position to be linked to other thiophene units during an
lectrochemical polymerization. However, the insolubility of theolymer film and its thinness will not allow the direct probing of theature of the polymer linkage by, for instance, NMR spectroscopy,ut Raman spectroscopic evidence provides clear indications of theonnectivity of the polymer.
To compare the bond stretches within the pTTP film withhose of the TTP monomer, we used Raman spectroscopy. Fig. 2hows the Raman spectra of TTP and pTTP (grown on an ITOlectrode). Both display some diagnostic bands corresponding toibrations of porphyrin macrocycle (970, 1242 and 1367 cm−1
or pTTP and 1000, 1240, 1370, 1448 and 1555 cm−1 for TTP)39]. However, several characteristic Raman peaks in the range of90–800 cm−1 are observed for pTTP, while they are absent in theTP monomer. Specifically, the peak at 705 cm−1 for pTTP, which isiagnostic for the C�–S–C�′ ring deformation mode in polymerized
hienyl groups [40], is absent in the spectrum of monomeric TTPonomers, but clearly present in pTTP, thus indicating that poly-erization, as predicted, had taken place via the �-positions of the
hienyl groups. The surface morphology of a pTTP film deposited onn ITO electrode was investigated by scanning electron microscopy
Scheme 2. Electrochemical p
Fig. 2. Raman spectra of TTP and pTTP on ITO glass. Excitation wavelength = 512 nm.
(SEM). Fig. 3 shows the comparison of representative SEM imagesof the bare ITO glass and the pTTP film. While the bare ITO glasspossesses a clean and smooth surface, the pTTP film is clearlyvisible and exhibits a dense morphology. Unlike the surface mor-phology of conventional conducting polymers such as polypyrrolethat show typical granular morphology [41,42], the surface of pTTPfilm is relatively smooth. Perhaps this is due to the fact that ide-ally TTP is polymerized along all four meso-thienyl groups, forminga 2-dimensional lattice [43]. The thickness of the layer after threevoltammetric cycles was ∼120 nm.
3.3. Voltammetric studies of 2,4-DNT on the pTTP-modified GCelectrode
To test the voltammetric reduction of explosives on the pTTP-modified GC electrode, 2,4-DNT was used as the first target. Fig. 4ashows the reduction peak region of the CV resulting from thepresence of 100 ppb 2,4-DNT using a bare GC electrode and a pTTP-modified GC electrode in 0.01 M pH 7 phosphate buffer at a scanrate of 50 mV/s. One can see that the reduction of 2,4-DNT on thepTTP-coated GC electrode shows two well-defined reduction peaks(peak I and peak II). In comparison, the reduction of 2,4-DNT on thebare GC electrode is barely noticeable, demonstrating that the pTTP
coating can greatly enhance the electrochemical reduction of 2,4-DNT. To answer the question whether it is the polythiophene phaseor the porphyrin of the pTTP coating that is responsible for theelectrocatalysis, we prepared a polythiophene-modified GC elec-trode and a TTP-modified GC electrode. Both modified electrodesolymerization of TTP.
194 W. Chen et al. / Sensors and Actuators B 147 (2010) 191–197
Fig. 3. Typical SEM images of (a) a bare ITO
Fig. 4. (a) Cyclic voltammograms (the reduction peaks region) at the bare GCelectrode (dash line) and the pTTP-modified GC electrode (solid line) for 100 ppb2,4-DNT in 0.01 M pH 7.0 phosphate buffer. Scan rate = 100 mV/s. (b) The reduc-tion peak currents of 100 ppb 2,4-DNT in 0.01 M pH 7.0 phosphate buffer versus thesquare root of scan rate for the reduction peak I (�) and II (�), respectively. (c) ThepH dependence of the peak potentials in 2,4-DNT reduction for the reduction peakI (�) and II (�), respectively.
glass and (b) pTTP film on ITO glass.
show a performance that is very similar to that of the bare electrode(Fig. 6), highlighting the crucial role the porphyrins incorporated inthe conducting chain play in the reduction of 2,4-DNT.
The electrochemical reduction of nitroaromatic compounds iswell understood [3,19,20,24]. Each peak corresponds to the sequen-tial reduction of one nitro group to generate hydroxylamines,followed by a total or partial reduction of the latter to amine groups(Eqs. (1) and (2)).
�-NO2 + 4e + 4H+ � �-NHOH + H2O (1)
�-NHOH + 2e + 2H+ � �- NH2 + H2O (2)
Prophyrins are electron-rich, while the 2,4-DNT is electron defi-cient due to the strong electron-withdrawing power of the twonitro groups. Therefore, the basis for a favorable �–� interactionbetween the pTTP and DNT, possibly enhanced by a charge-transfercomponent, are given. The resulting close contact of 2,4-DNT withthe conducting pTTP film enhances its electrochemical reduction.
The CV curves of the pTTP-modified GC electrode in 0.01 MpH 7.0 phosphate buffer containing 100 ppb 2,4-DNT were alsorecorded at various scan rates (�). The peak currents were plottedas a function of the square root of the scan rate (�1/2). As shownin Fig. 4b, both of the reduction peak currents are proportional to�1/2, showing that the reduction of 2,4-DNT on the pTTP-modifiedelectrode is a typical diffusion controlled electrochemical event.
The effect of pH on the reduction of 2,4-DNT is shown in Fig. 4c.A negative shift of reduction peak potential was observed with theincrease of the buffer pH values. A slope of −48.3 and −44.1 mV/pHwas obtained for reduction peaks I and II, respectively, indicatingthat the mechanism of both reduction processes involve approxi-mately the same number of electrons and protons. This finding isconsistent with the reductions along Eqs. (1) and (2), and is alsoconsistent with other reports [3,19,20,26].
3.4. 2,4-DNT detection on the pTTP-modified GC electrode
The detection of 2,4-DNT using DPV was optimized with respectto the CV deposition cycles of pTTP and the buffer pH value. Thethickness of the pTTP film is controlled by the number of CV depo-sition cycles: the larger of the number of CV deposition cycles, thethicker the deposited pTTP film. Fig. 5a shows the effect of theCV deposition cycles on the response to 1 ppm 2,4-DNT in buffer.The background-subtracted reduction peak current at peak I wasrecorded here. As expected, the response increased initially butreached a maximum at three cycles of CV deposition. More depo-sition cycles lead to a gradual signal decrease. The initial increaseis attributed to an enhanced catalytic activity and electron trans-
fer of the deposited pTTP, while the decrease at higher numbers ofCV deposition cycles is likely due to increased mass and electrontransport resistance caused by the rigid and thicker pTTP film. Thusthree CV deposition cycles were applied for the preparation of thepTTP-modified electrodes used in subsequent work.
W. Chen et al. / Sensors and Actuators B 147 (2010) 191–197 195
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Fig. 6. The calibration plots for 2,4-DNT on the pTTP-modified electrode (�),the bare GC electrode (�), the drop-cast TTP-modified GC electrode (�), and the
ig. 5. Optimization of 2,4-DNT reduction at the pTTP-modified GC electrode withespect to (a) the deposition cycles of pTTP film and (b) the buffer pH. The concen-ration of 2,4-DNT is 1 ppm. The reduction peak I was used here.
As the reduction of 2,4-DNT consumes protons (Eqs. (1) and (2)),he effect of pH on the response was also investigated to establishhe optimal assay pH value. As shown in Fig. 5b, the optimal pHalue for the assay is at pH 5.9. The electrochemical signal strengthf the reduction of 2,4-DNT decreases only slightly with a drop of pHut falls off sharply at pH values above of 7.0. Thus, as expected, highroton concentration generally favors the reduction of 2,4-DNT,nd the reduction is greatly inhibited in basic solution. However,hen the pH value is lower than the optimal pH, the reduction of
,4-DNT is slightly suppressed. This can be understood consideringhat a too low pH solution may protonate the free base of por-hyrin in the pTTP film [44], thus changing the charge status of theorphyrin and weakening its binding affinity to 2,4-DNT. AlthoughH 5.9 was determined to be the optimum pH for the operation,ubsequent experiments were still performed at the standard pH.0 because most of environmental samples have a pH value closeo neutral pH and also because there is no significant differencef the background-subtracted peak current at pH 7.0 and pH 5.9−0.336 �A vs. −0.355 �A).
The inset of Fig. 6 illustrates the differential pulse voltammetricesponse of the pTTP-modified electrode to successive addition of0 ppb 2,4-DNT aliquots under optimal detection conditions, alongith the voltammogram in buffer solution (background). The addi-
ion of 2,4-DNT results in well-defined reduction peaks and theeak currents are directly proportional to the analyte concentra-ion. The assay is sensitive. Even a concentration of 50 ppb 2,4-DNTauses a significant response without the need for any samplere-concentration. The peak current of peak I is, after background-
polythiophene-modified GC electrode (�). The current responses based on thereduction peak I are the values after background-subtraction. The inset displays thedifferential pulse voltammograms at the pTTP-modified GC electrode for increasinglevels of 2,4-DNT in steps of 50 ppb.
subtraction, used to construct a calibration curve, presented inFig. 6. The response of the pTTP-modified GC electrode increaseswith the analyte concentration but gradually levels off at a concen-tration above ∼250 ppb showing an expected saturation response.The limit of detection (LOD) was estimated to be 8 ppb 2,4-DNT(signal-to-noise ratio of 3).
To demonstrate the activity of the pTTP-modified GC electrode,a comparison to three electrodes was made: (1) a bare GC electrode,(2) a GC electrode upon which TTP monomer was drop-deposited,and (3) a polythiophene-modified GC electrode. Fig. 6 shows theresults. Compared to the response of the pTTP-modified GC elec-trode upon the increase of DNT, much smaller responses wererecorded for all other electrodes. These results indicate that pTTPcan significantly enhance the reduction of 2,4-DNT.
3.5. Detection of other explosives on the pTTP-modified GCelectrode
The pTTP-modified GC electrode was also evaluated againstother explosives under the standard conditions. Fig. 7a–d showthe dependence of the response to increasing concentrations ofTNT, Tetryl, RDX, and nitromethane (the reduction peak I at −0.56,−0.45, −0.83 and −0.8 V were plotted, respectively). The insetsof Fig. 7 present the DPV responses. The pTTP-modified GC elec-trode displays a wide dynamic range with good sensitivity for thenitroaromatic compounds TNT and Tetryl. The LOD was 8 ppb ofTNT and 9 ppb of Tetryl, respectively. In addition, the pTTP filmalso displayed good sensitivity for the alkylnitro compounds RDXand nitromethane, with the LOD of 96 and 43 ppb, respectively.These values are comparable to, or better than, the values forother reported explosives sensors [2,5,6,19,20,26,45–47]. There isno significant response for the investigated analytes on the con-trol electrodes (bare GC, TTP-modified, polythiophene-modified;data not shown). The LODs for nitromethane and RDX are oneorder of magnitude higher than those for 2,4-DNT, TNT, and Tetryl.The better detection limits for the nitroaromatic compounds may
be attributed to the fact that the nitroaryls are generally easilyreduced than nitroalkanes. Further, the affinity of the aromatic por-phyrins for nitroaromatic compounds is expected to be higher thanfor nitroalkanes. The pTTP-modified electrodes are stable. Afterthe sensing experiments, the pTTP electrodes were rinsed with
196 W. Chen et al. / Sensors and Actuators B 147 (2010) 191–197
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ig. 7. Calibration plots for (a) TNT, (b) Tetryl, (c) RDX, and (d) nitromethane on thefter background-subtraction. The insets show the original DPV data.
ater and used for numerous additional measurements withoutny apparent loss in performance.
. Conclusions
In summary, conducting pTTP films made by electropolymer-zation of the thienyl-derivatized porphyrin TTP onto GC electrodesossess excellent mechanical and electrical properties. Most signif-
cantly, the pTTP-modified GC electrodes can significantly enhancehe electrochemical reduction of the common explosives 2,4-DNT,NT, Tetryl, RDX, and nitromethane in 0.01 M pH 7.0 phosphateuffer solutions. We attribute this to the affinity of the porphyrin inhe polymer backbone for the analytes and its electrocatalytic prop-rties. The modified electrode has a good response, dynamic range,nd high sensitivity without the need for pre-concentration steps orsing anodic stripping techniques. These features, combined withhe ease of their preparation, make the novel conducting pTTP filmn attractive electrode material for the detection of explosives inqueous solutions.
cknowledgments
We greatly appreciate the funding from NSF and Science andechnology Directorate of the U.S. Department of Homeland Secu-ity. We thank Joshua Akhigbe for the preparation of TTP. “Pointsf view in this document are those of the author(s) and do notecessarily represent the official position of the funding agencies.”
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iographies
ei Chen is a postdoctoral fellow in the Department of Chemical, Materials andiomolecular Engineering, University of Connecticut (UConn). He earned his PhDegree in 2008 in Bioengineering at Nanyang Technological University, Singapore.is research interests are centered on the electrochemical detection of biomarkersnd explosives.
tors B 147 (2010) 191–197 197
Ying Wang is a graduate student at UConn, Department of Chemical, Materials andBiomolecular Engineering. She earned a Master degree in 2007 in Chemical andBiomolecular Engineering at Xiamen University, China. Her PhD research concen-trates on the development of electrical and electrochemical sensors for explosivecompounds.
Changming Li is a professor of Bioengineering at Nanyang Technological University,Singapore. He received his PhD in Analytical Chemistry from Wuhan University,China, in 1987. His research is focused on engineering applications of bio- andnanotechnology, including microfluidics, biosensors, fuel cells, and biomaterials.
Christian Brückner is an associate professor of Chemistry at UConn. He received in1996 his PhD in Organic Chemistry from the University of British Columbia, Canada.His research interests lie in synthetic porphyrin chemistry and the application ofporphyrinoids as functional dyes in chemosensing, photodynamic cancer therapy,or as fluorescent markers.
Yu Lei is an assistant professor of Chemical, Materials and Biological Engi-neering at UConn. Dr. Lei obtained his PhD degree in 2004 at the Universityof California-Riverside in Chemical and Environmental Engineering. His currentresearch combines biotechnology, nanotechnology, and sensing technology, espe-cially as applied to the development of gas sensors, electrochemical sensors, andbiosensors.