A simple and cost-effective, all-electrochemical method to fabricate and assemble single conducting polymer nanowire based biosensors was developed. Polypyrrole (Ppy) nanowires were synthesized by electrochemical polymerization using an alumina template. The single-nanowire chemoresistive sensor device was assembled using ac dielectrophoretic alignment followed by maskless anchoring on a pair of gold electrodes separated by 3 microm. To establish an efficient covalent surface biofunctionalization route, glutaraldehyde (GA) and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) chemistries were compared. EDC was established to be the most effective chemistry and was used to surface-functionalize a single Ppy nanowire with cancer antigen (CA 125) antibody to fabricate a nanoimmunosensor for CA 125 biomarker detection and quantification. The immunosensor had excellent sensitivity with a lower detection limit of 1 U/mL CA 125 and dynamic range up to 1000 U/mL in 10 mM phosphate buffer. Furthermore, there was no loss of performance upon exposure to CA 125 in spiked human blood plasma. This demonstrates the clinical importance of these sensors for cancer marker detection with cost benefits and great portability for diagnosis of patients at the point of care.

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We have fabricated a highly sensitive, simple and label-free single polypyrrole (Ppy) nanowire based conductometric/chemiresistive DNA sensor. The fabrication was optimized in terms of probe DNA sequence immobilization using a linker molecule and using gold-thiol interaction. Two resultant sensor designs working on two different sensing mechanisms (gating effect and work function based sensors) were tested to establish reliable sensor architecture with higher sensitivity and device-to-device reproducibility. The utility of the work function based configuration was demonstrated by detecting 19 base pair (bp) long breast cancer gene sequence with single nucleotide polymorphism (SNP) discrimination with high sensitivity, lower detection limit of~10 À16 M and wide dynamic range (~10 À16 to 10 À11 M) in a small sample volume (30 mL). To further demonstrate the utility of the DNA sensor for detection of target sequences with different number of bases, targets with 21 and 36 bases were detected. These sequences have implications in environmental sample analysis or metagenomics. Sensor response showed increase with the number of bases in the target sequence. For long sequence (with 36 bases), effect of DNA alignment on sensor performance was studied.

We report development, characterization and testing of chemiresistive immunosensors based on single polypyrrole (Ppy) nanowire for highly sensitive, specific, label free, and direct detection of viruses. Bacteriophages T7 and MS2 were used as safe models for viruses for demonstration. Ppy nanowires were electrochemically polymerized into alumina template and single nanowire based devices were assembled on a pair of gold electrodes by ac dielectrophoretic alignment and anchored using maskless electrodeposition. Anti-T7 or anti-MS2 antibodies were immobilized on single Ppy nanowire using EDC-NHS chemistry to fabricate nano-biosensor for the detection of corresponding bacteriophage. The biosensors showed excellent sensitivity with a lower detection limit of 10−3 plaque forming unit (PFU) in 10 mM phosphate buffer, wide dynamic range and excellent selectivity. The immunosensors were successfully applied for the detection of phages in spiked untreated lake water samples. The results show the potential of these sensors in health care, environmental monitoring, food safety and homeland security for sensitive, specific, rapid and affordable detection of bioagents/pathogens.