 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
Tissue Implantable Biomedical Sensors
National Science Foundation
Paul Barone, Daniel Heller, Dr. Seunghyun Baik
Molecular detection using near-infrared light between 0.9 and 1.3 eV has important biomedical applications because of greater tissue penetration and reduced autofluorescent background in thick tissue or whole-blood media. Carbon nanotubes have a tunable near-infrared emission that responds to changes in the local dielectric function but remains stable to permanent photobleaching. In this work, we report the synthesis and successful testing of solution-phase, near-infrared sensors, with beta-D-glucose sensing as a model system, using single-walled carbon nanotubes that modulate their emission in response to the adsorption of specific biomolecules. New types of non-covalent functionalization using electron-withdrawing molecules are shown to provide sites for transferring electrons in and out of the nanotube. We also show two distinct mechanisms of signal transduction - fluorescence quenching and charge transfer. The results demonstrate new opportunities for nanoparticle optical sensors that operate in strongly absorbing media of relevance to medicine or biology.
PW Barone, S Baik, DA Heller, MS Strano: Near-infrared optical sensors based on single-walled carbon nanotubes. Nature Materials 4 (2005) 86-92.
PW Barone, RS Parker, MS Strano: In vivo fluorescence detection of glucose using a single-walled carbon nanotube optical sensor: design, fluorophore properties, advantages, and disadvantages. Analytical Chemistry 77 (2005) 7556-62.
Sub-cellular Sensors based upon Solvatochromism
National Institutes of Health, Beckman Young Investigator Award
Daniel Heller, Hong Jin, Dr. Jong Hyun Choi
The optical transition energies (E ii) of single-walled carbon nanotubes (SWNT) are influenced by the local environment created by solvents or other adsorbed molecules. We analyze the emission energies of SWNT photoluminescence (PL) in various dielectric media, and elucidate a 1/R 4 scaling of the transition polarizability from a classical solvatochromic formalism. This solvatochromic shift is shown to vary inversely with the square of the of the transition energy, as predicted by theory and ab-initio calculations . SWNT band-gap fluorescence undergoes a red shift when an encapsulating 30-nucleotide oligomer is exposed to counter ions that screen the charged backbone. The transition is thermodynamically identical for DNA on and off the nanotube, except that the propagation length of the former is shorter by five-sixths. The magnitude of the energy shift is described by using an effective medium model and the DNA geometry on the nanotube sidewall. We demonstrate the detection of the B-Z change in whole blood, tissue, and from within living mammalian cells.
DA Heller, ES Jeng, TK Yeung, BM Martinez, AE Moll, JB Gastala, MS Strano: Optical detection of DNA conformational polymorphism on single-walled carbon nanotubes. Science 311 (2006) 508-11.
Optical Transduction from Aptamer-Capped Nanocrystal Quantum Dots
Beckman Institute Seed Grant
Dr. Jong Hyun Choi
We demonstrate that aptamer-capped near-infrared PbS quantum dots (QDs) can detect a target protein based on selective charge transfer. The water-soluble QDs are synthesized with the thrombin-binding aptamer, which retains the secondary quadruplex structure necessary for binding to thrombin. These QDs have diameters of 3-6 nm and fluoresce around 1050 nm. When the aptamer-functionalized QD binds to its target, a fluorescence quenching occurs due to charge transfer from amine groups on the protein to the QD. Thrombin is detected within 1 min with a detection limit of ~1 nM. This selective detection is observed even in the presence of high background concentrations of interfering negatively or positively charged proteins, suggesting that aptamer-capped QDs could be useful for label-free protein assays.
JH Choi, KH Chen, MS Strano: Aptamer-capped nanocrystal quantum dots: A new method for label-free protein detection. Journal of the American Chemical Society 128 (2006) 15584-85.
Structure-Reactivity Relationships for Carbon Nanotubes
Intel; 3M
Nitish Nair, Monica Usrey, Dr. Woo Jae Kim
Structure-reactivity relationships for electron-transfer reactions of single walled carbon nanotubes (SWNTs) are derived and experimentally validated for the first time using 4-hydroxybenzene diazonium as a model electron acceptor. The model describes steady-state reaction data using an adsorption-controlled scheme, and electron transfer theories are used to explain the difference in reactivities between different nanotube chiralities. The formalism provides a mechanistic insight into electronically selective reactions of SWNT. Current research seeks to extend these relationships for a wide range of electron acceptors.
N Nair , WJ Kim, ML Usrey, MS Strano: A structure-reactivity relationship for single walled carbon nanotubes reacting with 4-hydroxybenzene diazonium salt. Journal of the American Chemical Society 129 (2007) 3946-54.
ML Usrey, ES Lippmann, MS Strano: Evidence for a two-step mechanism in electronically selective single-walled carbon nanotube reactions. Journal of the American Chemical Society 127 (2005) 16129-35
Chemical Separation of Carbon Nanotubes
American Chemical Society PRF, Intel
Dr. Woo Jae Kim, Nitish Nair, Monica Usrey
p-Hydroxybenzene diazonium salt was utilized to selectively functionalize metallic single-walled carbon nanotubes (SWNT) at 45 degrees C with high selectivity. Deprotonation in alkaline solution induces a negative charge on the functionalized SWNT for electrophoretic separation. We applied this concept to enrich metallic and semiconducting fractions separately using the induced differences in electrophoretic mobilities. Free solution electrophoresis was utilized to separate selectively reacted samples into nonmobile and negative electrophoretic mobility fractions. Raman spectroscopy and UV-vis-nIR absorption spectroscopy confirm both the separation of reacted and unreacted SWNT, and after annealing, the enrichment of metallic and semiconducting SWNT respectively in two distinct fractions. Future work focuses on the scaling of this process.
WJ Kim, ML Usrey, MS Strano: Selective functionalization and free solution electrophoresis of single-walled carbon nanotubes: separate enrichment of metallic and semiconducting SWNT. Chemistry of Materials 19 (2007) 1571-1576.
Engineering Reversible and Irreversible Chemical Adsorption Sites on Nanotube Electronic Array Sensors
Department of Homeland Security
Chang Young Lee, Richa Sharma
A wide range of analytes adsorb irreversibly to the surfaces of single walled carbon nanotube electronic networks typically used as sensors or thin-film transistors, although to date the mechanism is not understood. Using thionyl chloride as a model electron-withdrawing adsorbate, we show that reversible adsorption sites can be created on the nanotube array via noncovalent functionalization with amine-terminated molecules of pK a < 8.5. A nanotube network comprised of single, largely unbundled nanotubes, near the electronic percolation threshold is required for the effective conversion to a reversibly binding array. X-ray photoelectron spectroscopy (XPS) and molecular potential calculations confirm that adsorption takes place on the amine layer. By examining 11 types of amine-containing molecules, we show that analyte adsorption is largely affected by the basicity (pK b) of surface groups. The binding energy of the analyte is apparently reduced by its adsorption on the surface chemical groups instead of directly on the SWNT array itself. This mediated adsorption mechanism is supported by XPS and molecular potential calculations. Reversible detection with no active regeneration at parts-per-trillion level is demonstrated for the first time by creating a higher adsorption site density with a polymer amine, such as polyethyleneimine ( PEI).
CY Lee, MS Strano: Understanding the dynamics of signal transduction for adsorption of gases and vapors on carbon nanotube sensors. Langmuir 21 (2005) 5192-96.
An On-Chip Gas Chromatograph using Carbon Nanotube Electronic Arrays
DARPA (w/ R. Masel, UIUC)
Chang Young Lee, Dr. J. Zhang
Laboratory gas chromatograph with mass spectroscopic detection remains the definitive analytical determinant of a wide range of important molecules including chemical weapons and explosive residues. We consider the prospect of miniaturizing this process down to microfluidic scales. Viable micro gas chromatography (µGC) column designs have been recently demonstrated. The feasibility of on-chip µGC, however, depends upon a new generation of ultra-fast and sensitive detection technologies capable of microfluidic integration with low power consumption. Towards this end, the Strano group has pioneered the concept of chemically tuning molecular adsorption on single walled carbon nanotube electronic chemi-resistor arrays to enable rapid molecular transduction with ppt level detection sensitivity. We have demonstrated, for the first time, that analysis of a microfluidic peak train is possible. Our present goal, in collaboration with the Swager research group at MIT, is to understand the molecular transduction process on these arrays more completely and develop chemical interfaces that impart reversible and selective adsorption with low detection limits for a generic suite of target molecules.
CY Lee, S Baik, J Zhang, RI Masel, MS Strano: Charge Transfer from metallic single-walled carbon nanotube sensor arrays. Journal of Physical Chemistry B 110 (2006) 11055-61
