Tapan Sarkar

Label-free chemiresistive biosensor for mercury (II) based on single-walled carbon nanotubes and structure-switching DNA

Herein, we present a sensitive, selective, and facile label-free DNA functionalized single-walled carbon nanotube (SWNT)-based chemiresistive biosensor for the detection of Hg(2+). SWNTs were functionalized with Hg(2+) binding 15-bases long polyT oligonucleotide through covalent attachment using a bilinker molecule. The polyT was further hybridized with polyA to form a polyT-polyA duplex. When exposed to Hg(2+) the polyT-polyA duplex was dehybridized combined with switching of polyT structure, leading to change in resistance/conductance of the SWNT chemiresistor device. The device provided a significant response within 100 to 1000 nM of Hg(2+) concentration with a 6.72 × 10(-3) nM(-1) sensitivity.

Carbon Nanotubes-Based Label-Free Affinity Sensors for Environmental Monitoring

Nanostructures, such as nanowires, nanobelts, nanosprings, and nanotubes, are receiving growing interest as transducer elements of bio/chemical sensors as they provide high sensitivity, multiplexing, small size, and portability. Single-walled carbon nanotubes (SWNTs) are one such class of nanostructure materials that exhibit superior sensing behavior due to its large-surface carbon atoms that are highly responsive to surface adsorption events. Further, their compatibility with modern microfabrication technologies and facile functionalization with molecular recognition elements make them promising candidates for bio/chemical sensors applications. Here, we review recent results on nanosensors based on SWNTs modified with biological receptors such as aptamers, antibodies, and binding proteins, to develop highly sensitive, selective, rapid, and cost-effective label-free chemiresistor/field-effect transistor nanobiosensors for applications in environmental monitoring.

A miniature chemiresistor sensor for carbon dioxide.

A carpet-like nanostructure of polyaniline (PANI) nanothin film functionalized with poly(ethyleneimine), PEI, was used as a miniature chemiresistor sensor for detection of CO2 at room temperature. Good sensing performance was observed upon exposing the PEI-PANI device to 50-5000 ppm CO2 in presence of humidity with negligible interference from ammonia, carbon monoxide, methane and nitrogen dioxide. The sensing mechanism relied on acid-base reaction, CO2 dissolution and amine-catalyzed hydration that yielded carbamates and carbonic acid for a subsequent pH detection. The sensing device showed reliable results in detecting an unknown concentration of CO2 in air.

Photo-induced charge transport in ZnS nanocrystals decorated single walled carbon nanotube field-effect transistor

We describe a photoresponse measurement study on a pyrene linked ZnS nanoparticles decorated single walled carbon nanotube (SWNT) field-effect transistor (FET). We observed that the photocurrent response in the system is based on the semiconducting property of the SWNT. It was found that both the organic molecule linker, pyrene, together with ZnS nanocrystals contributed to the total photoresponse of the ZnS-pyrene/SWNT hybrid device. We demonstrated by FET characteristic studies that the majority charge carriers in the ZnS-pyrene/SWNT device upon UV illumination are positively charged photo-induced holes near the p-type SWNT channel.

Potassium Iodide-Functionalized Polyaniline Nanothin Film Chemiresistor for Ultrasensitive Ozone Gas Sensing

Polyaniline (PANI) nanostructures have been widely studied for their sensitivity to atmospheric pollutants at ambient conditions. We recently showed an effective way to electropolymerize a PANI nanothin film on prefabricated microelectrodes, and demonstrated its remarkable sensing performance to be comparable to that of a one-dimensional nanostructure, such as PANI nanowires. In this work, we report further progress in the application of the PANI nanothin film chemiresistive sensor for the detection of ozone (O3) by modifying the film with potassium iodide (KI). The KI-PANI sensor exhibited an excellent sensitivity to O3 (8–180 ppb O3 concentration rage) with a limit of detection of 230 ppt O3, and exquisite selectivity against active chemicals such as nitrogen dioxide (NO2) and sulfur dioxide (SO2). The sensing mechanism of the sensor relied on iodometric chemistry of KI and O3, producing triiodide (I3−) that partially doped and increased electrical conductivity of the PANI film. The sensitivity and selectivity of the KI-functionalized PANI film demonstrates the potential use for KI-PANI-based O3 sensing devices in environmental monitoring and occupational safety.

Volatile Organic Compounds

Detection and quantification of volatile organic compounds (VOCs) are basic and necessary requirements for many applications, including environmental monitoring, occupational safety, and healthcare. Many toxic and/or carcinogenic VOCs are used as solvents and base raw materials in chemical process industries. For example, ketones (acetone and methylethyl ketone), alkanes (hexane), alcohols (ethanol), and aromatics (benzene and toluene) are widely used as a solvent, and formaldehyde is used as a base raw material for the resin industry. Benzene, toluene, ethylbenzene, and xylenes (commonly known as BTEX compounds) are released in automobile exhaust gas. Further, some VOCs have been identified as potential biomarkers of diseases in exhaled breath, such as alkanes and benzene derivatives for lung cancer and acetone for diabetes. Hence accurate identification and quantification of these VOCs is a must to protect the human health at work place, environment, and disease diagnosis.