molecule probes for trace detection of metal ionslzang/images/poster-molecular-probes.pdf ·...
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Molecule Probes for Trace Detection of Metal IonsHigh Resolution Imaging at both Large-area and Single-molecule Scale
The Zang Research Group, Department of Materials Science and EngineeringTel. 801-587-1551, Email: [email protected], Web: www.eng.utah.edu/~lzang
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Why at Single-Molecule?(for high resolution and more detailed information)
• Remove ensemble averaging of bulk phase measurement: creating a frequency histogram of the actual distribution of values for an experimental parameter (wavelength or intensity) --- the probability distribution function.Examples: surface probing, enzyme or protein labeling.
• Reveal and diagnose the events of extremely low probability: repeatedly excitation of one molecule or measuring hundreds of different molecules. Statistics provides occurrence probability distribution as a function of structures or local environments.Examples: slow charge transfer (see next slide).
• Remove the need for synchronization of many single molecules undergoing a time-dependent process (e.g. charge or energy transfer). Examples: an enzyme in several catalytic state, multiple-chromophore supramolecules, proteins in different conformations. (see the attached slide).
• Monitor quantum-size effect of semiconductor nanoparticles in combination with NSOM technique: direct correlation between optical properties and particle size. Remove the tough requirement for narrow size distribution, which is usually difficult to obtain for particle smaller than 10 nm.
• Represent the ultimate level of detection sensitivity and device miniaturization.
A distribution contains more information than the average value alone!
When ket << kisc + kic + krIt is impossible to measure ket via bulk phase methods.
Near-field scanning optical microscope (NSOM)scanning confocal microscope (SCM)
A robust probe for selective detection of Zn2+
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NH N
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Zn2+
zinc
Non-emitting
Emitting
Hg2+ (3.5 µM)
other metal ions (12.5 µM)
Ultra-selective Fluorescent Sensing of Hg2+
ChemComm. 2008, 1413-1415. Featured as a Hot Article.
Single Molecule Imaging: revealing rare events.
P—P Pdead—Pdead
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P+—P-
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e-
J. Am. Chem. Soc. 126 (2004) 16126 -16133.Determines changes in distance (conformation) rather than absolute distances as ‘E’ depends on orientation of the dyes. FRET is particularly useful for biological systems. most of smFRET studies have been performed on bio-molecules.
From Ha lab @ UIUC
Spatial Gauging at Single-molecule Level: FRET (fluorescence resonant energy transfer)
Mercury (Hg2+)• A highly toxic metal ion, causes serious health and environment problems.
• Although many kinds of chemical and physical sensors (particularly the fluorescence based sensors) have been developed for the detection of Hg2+, it remains challenging how to improve the detection selectivity against the interference from the coexisting metal ions.
• Indeed, the concentrations of the common coexisting metal ions are usually much higher than the concentration of Hg2+, for which the safety level set up for drinking water by EPA is only 2 ppb (or 10 nM).
• To detect such trace amount of Hg2+ with minimal false positive requires a sensor technique with extremely high selectivity.
• An ideal fluorescence sensor system should be highly stable against photobleaching to minimize the false positive.
• The fluorescence sensor materials developed from our lab have proven robust against photobleaching, while still providing the unprecedented detection selectivity and sensitivity (down to ppt range).
Zinc (Zn2+)• An essential nutrient sustaining all forms of life.
• The second most abundant transition metal in the human body (2-3 g), playing pivotal roles in many cellular processes and functions.
• Structural cofactor in enzymes and other proteins.
• Released upon neuronal activity, likely mediating synaptic plasticity.
• Irregularity of Zn2+ (e.g., change in concentration) is correlated to several major diseases including Alzheimer’s disease, prostate cancer, and diabetes.
• Although many molecular fluorescence probes have been developed for efficient and selective detection of Zn2+, the photostability (against photobleaching) still remains a problem, which often draws back their real application in clinics.
• Since cell imaging, particularly those concerned cellular dynamics, takes time, a robust molecular probe, is strongly demanded.
Fluorescence Spectra upon presence of Hg2+ High selectivity for Hg2+
With different R-groups, probing Zn2+ in different locations in living cells.
Fluorescence image
Fluorescence fluctuation monitored with photon counting and spectrarecording: extracting kinetics information for the ON and OFF states.
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Zn2+ concentration15 µM 8 µM 7 µM 6 µM 5 µM 4 µM 3 µM 2 µM 1 µM 0 µM
probe conc.: 15 µM
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Fluorescence titration with Zn2+
Single-Molecule Imaging and Probing
Single-moleculeprobe