Jay L. Snyder

Robust gold nanoparticles stabilized by trithiol for application in chemiresistive sensors

The use of gold nanoparticles coated with an organic monolayer of thiol for application in chemiresistive sensors was initiated in the late 1990s; since then, such types of sensors have been widely pursued due to their high sensitivities and reversible responses to volatile organic compounds (VOCs). However, a major issue for chemical sensors based on thiol-capped gold nanoparticles is their poor long-term stability as a result of slow degradation of the monothiol-to-gold bonds. We have devised a strategy to overcome this limitation by synthesizing a more robust system using Au nanoparticles capped by trithiol ligands. Compared to its monothiol counterpart, the new system is significantly more stable and also shows improved sensitivity towards different types of polar or non-polar VOCs. Thus, the trithiol-Au nanosensor shows great promise for use in real world applications.

Estimating Service Lives of Organic Vapor Cartridges III: Multiple Vapors at All Humidities

A widely used equation model for estimating service lives of organic vapor air-purifying respirator cartridges has been updated with more recent research results. It has been expanded to account for effects of high relative humidities. Adsorption capacity competition between water vapor and organic vapor is largely explained by mutual exclusion of adsorption volume of the activated carbon. The Dubinin/Radushkevich equation is used to describe the adsorption isotherms of both water and organic vapors. Effects of relative humidity and adsorbed water on adsorption rates are described by an empirical correlation with breakthrough times. The dynamic natures of adsorption and competition are incorporated using an expanding zone model with displaced water rollup. The complete model has been tested and verified with published and unpublished data from many sources.

Volatile organic compound discrimination using nanostructured polythiophene sensors

New synthesis methods have allowed us to make many semiconducting polythiophenes polymers with different side and end groups. Also, co-polymers combining a polythiophene chain attached to another polymer chain were synthesized. This design freedom brings a new dimensionality to the sensing properties of the materials. Single chip micro sensor resistor arrays, utilizing multiple polymers, were fabricated and then tested in an automated system. The sensors demonstrated ppm level sensitivity to various volatile organic compounds (VOCs) including both polar and non-polar materials. Polymers with different chemical structures show strong selectivity to different VOCs. By applying pattern recognition algorithms, the sensor response clearly discriminates between the tested VOCs allowing us to conjecture as to the role molecular modification have in determining response to specific VOCs

Nanostructure Dependence of Conductive Polymer Chemical Sensors

It is shown that the resistive sensing properties of conductive polymers are highly dependent on the material nanostructure. The sensing properties of regioregular poly(3-hexylthiophene) (P3HT) polymer thin films with porous nanofibrile structure, dense nanofibrile structure and nano-granular structure show very different conductance changes, in terms of both response amplitude and sign, upon exposure to various VOC vapors. This implies that multiple sensing mechanisms, such as both grain boundary and intra-grain effects, exist and the dominant sensing mechanism can vary with different material nanostructures. Possible mechanisms for these effects, and their correlation with observed material nanostructures, are also discussed.

Pilot Study of Aromatic Hydrocarbon Adsorption Characteristics of Disposable Filtering Facepiece Respirators that Contain Activated Carbon

Disposable filtering facepiece respirators (FFRs) used by health care workers are not designed to reduce the inhalation of volatile organic compounds (VOCs). Smoke-generating surgical procedures release VOCs and have been associated with the following complaints: foul smell, headaches, nausea, irritated throat and lungs, and asthma. Organic vapor FFRs that contain activated carbon are used by industrial workers to provide odor relief. These respirators remove irritating odors but are not marketed as respirators that provide respiratory protection against a gas or vapor. This study investigated the aromatic hydrocarbon adsorption capabilities of nuisance organic vapor (OV) FFRs. Three OV FFR models were tested to determine the 10% breakthrough time of three aromatic hydrocarbons at ambient room temperature and relative humidity. All respirator models were exposed to each vapor separately in three duplicate tests (n = 27). The respirator was sealed with silicone to an AVON-ISI headform that was placed in a chamber and exposed to VOC-laden air (20 ppm, 37 L/min). Periodically, gas samples were directed to an SRI gas chromatograph (Model 8610C) for analysis. All respirators performed similarly. The average 10% breakthrough values for all tests were at least 64 min, 96 min, and 110 min for benzene, toluene, and xylene, respectively. Respirators were tested with challenge concentrations at nuisance levels (20 ppm) and did not exceed 10% breakthrough values for at least 61 min. While the results of this pilot study hold promise, there is a need for further investigation and validation to determine the effectiveness of nuisance FFRs in mitigating organic vapors such as benzene, toluene, and xylene.

Development of an Inexpensive RGB Color Sensor for the Detection of Hydrogen Cyanide Gas

An inexpensive red, green, blue (RGB) color sensor was developed for detecting low ppm concentrations of hydrogen cyanide gas. A piece of glass fiber filter paper containing monocyanocobinamide [CN(H2O)Cbi] was placed directly above the RGB color sensor and an on chip LED. Light reflected from the paper was monitored for RGB color change upon exposure to hydrogen cyanide at concentrations of 1.0-10.0 ppm as a function of 25%, 50%, and 85% relative humidity. A rapid color change occurred within 10 s of exposure to 5.0 ppm hydrogen cyanide gas (near the NIOSH recommended exposure limit). A more rapid color change occurred at higher humidity, suggesting a more effective reaction between hydrogen cyanide and CN(H2O)Cbi. The sensor could provide the first real time respirator end-of-service-life alert for hydrogen cyanide gas.

Regioregular polythiophene nanowires and sensors

We have developed and synthesized highly conductive regioregular poly(3-alkylthiophene) (rr-PAT) derivatives for use in sensor arrays on a chip. Poly(3-alkylthiophene)s are ideally suited for this application because of their excellent electrical properties, solution processability and our ability to modify their chemical structure. Here, we synthesized rr-PATs that have different side chains and different end groups. The polymers were ink-jetted onto ChemFET devices on a chip and their chemical sensing properties were tested to a variety of volatile organic compounds (VOCs). The sensors demonstrated ppm level sensitivity and selectivity to all VOCs tested, including both polar and non-polar compounds.