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Thin-film silicon ISFETs for DNA and protein detection
Electrolyte-gate amorphous silicon thin film transistors (EG-TFTs) are used for pH sensing and detection of DNA and proteins (horseradish peroxidase, HRP). The sensing layer used was SiNx or SiO2. Measurements are performed with an external Ag/AgCl micro-reference electrode immersed in 100 mL of electrolyte solution. The devices show linear sensitivity to pH above the point of zero charge and respond to the adsorption of oligonucleotides and HRP with typical Langmuir adsorption behavior. DNA immobilization and hybridization detection is demonstrated. Voltage shifts of the transfer curves of the devices are observed resulting from successive steps of surface functionalization, covalent DNA attachment to the functionalized surface, surface blocking, and hybridization with a complementary target. The average voltage shifts upon immobilization are of the order of -880 mV and upon hybridization, around -90 mV. The reaction of a 50% non-complementary target leads to a voltage shift that is 43% smaller than that obtained for the hybridization with a fully complementary target. The hybridization reaction is confirmed by fluorescence microscopy. Surface control and reproducibility issues are addressed by the measurement of surface contact angles.
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Amorphous silicon ISFET is sensitive to unlabeled DNA and proteins. |
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