An embedded polymer piezoresistive microcantilever sensor

Label-free target DNA recognition using oligonucleotide-functionalized polypyrrole nanotubes

Conjugated polymers for oligonucleotide immobilization offer extraordinary potential as transducers for detecting DNA duplex formation, because the electrical, optical, and electrochemical properties are strongly affected by relatively small perturbations. Moreover, carboxylated conducting polymer supports are an attractive alternative due to their versatile immobilization with DNA, protein, and enzyme using various pendant groups: -SH, -NH(2), and -COOH. Therefore, we report the fabrication of carboxylic acid-functionalized polypyrrole nanotubes (CPPy NTs) using oxidant-impregnated template synthesis. The diverse number of carboxylates on the surface of CPPy NTs was applied to binding sites for amino-terminal oligonucleotides. Conductance of single DNA strands (ssDNA) and hybridized DNA helix were readily measured by means of depositing DNA-functionalized nanotubes on gold leads, and indicated high sensitivity (DeltaR/R(0)=1.7) even at low concentration (1 nmol) of target DNA. In addition, target DNA concentration was distinguished up to a narrow difference of 2 nmol. The successful DNA immobilization on polymer nanotubes was confirmed and visualized by the photoluminescence of fluorescein isothiocyanate (FITC)-tagged target DNA using confocal laser scanning microscopy.

Human hydration level monitoring using embedded piezoresistive microcantilever sensors

Embedded piezoresistive microcantilever (EPM) sensors were used to measure osmolality changes in both saliva mimic solutions and true human saliva. Osmolality changes in human saliva or urine may prove to be reliable, simple, and easy to measure markers for tracking human hydration levels. EPM sensors used in these experiments show good response to osmolality changes in both NaCl-based saliva mimic solutions and to human saliva. The addition of zero-point offset correction to EPM sensors allows for tracking of saliva osmolality changes with high accuracy. Also, the same EPM sensors exhibit a large enough range of osmolality response to make them potentially suitable for urine or blood serum osmolality monitoring.

Models of Hydrogel Swelling with Applications to Hydration Sensing

Hydrogels, polymers and various other composite materials may be used in sensing applications in which the swelling or de-swelling of the material in response to some analyte is converted via a transducer to a measurable signal. In this paper, we analyze models used to predict the swelling behavior of hydrogels that may be used in applications related to hydration monitoring in humans. Preliminary experimental data related to osmolality changes in fluids is presented to compare to the theoretical models. Overall, good experimental agreement with the models is achieved.

Mechano-transduction of DNA hybridization and dopamine oxidation through electrodeposited chitosan network

While microcantilevers offer exciting opportunities for mechano-detection, they often suffer from limitations in either sensitivity or selectivity. To address these limitations, we electrodeposited a chitosan film onto a cantilever surface and mechano-transduced detection events through the chitosan network. Our first demonstration was the detection of nucleic acid hybridization. In this instance, we electrodeposited the chitosan film onto the cantilever, biofunctionalized the film with oligonucleotide probe, and detected target DNA hybridization by cantilever bending in solution (static mode) or resonant frequency shifts in air (dynamic mode). In both detection modes, we observed a two-order of magnitude increase in sensitivity compared to values reported in literature for DNA immobilized on self-assembled monolayers. In our second demonstration, we coupled electrochemical and mechanical modes to selectively detect the neurotransmitter dopamine. A chitosan-coated cantilever was biased to electrochemically oxidize dopamine solution. Dopamine's oxidation products react with the chitosan film and create a tensile stress of approximately 1.7 MPa, causing substantial cantilever bending. A control experiment was performed with ascorbic acid solution. It was shown that the electrochemical oxidation of ascorbic acid does not lead to reactions with chitosan and does not change cantilever bending. These results suggest that chitosan can confer increased sensitivity and selectivity to microcantilever sensors.