DEVELOPING PROBES FOR LABEL-FREE DETECTION OF HEXANUCLEOTIDE GGGGCC REPEATS BY ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY

DNA repeat expansion sequences cause a myriad of neurological diseases when they expand beyond a critical threshold. Previous electrochemical approaches focused on the detection of trinucleotide repeats (CAG, CGG, and GAA) and relied on labeling of the probe and/or target strands or enzyme-linked assays. However, detection of expanded GC-rich sequences is challenging because they are prone to forming secondary structures such as cruciforms and quadruplexes. Here, we present label-free detection of hexanucleotide GGGGCC repeat sequences, which cause the leading genetic form of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). The approach relies on capturing targets by surface-bound oligonucleotide probes with a different number of complementary repeats, which proportionately translates the length of the target strands into charge transfer resistance (RCT) signal measured by electrochemical impedance spectroscopy (EIS). The probe carrying three tandem repeats transduces the number of repeats into RCT with a 3× higher calibration sensitivity and detection limit. Chronocoulometric measurements show a decrease in surface density with increasing repeat length, which is opposite of the impedance trend. This implies that the length of the target itself can contribute to amplification of the impedance signal independent of the surface density. Moreover, the probe can distinguish between a control and patient sequences while remaining insensitive to non-specific Huntington’s disease (CAG) repeats in the presence of a complementary target. This label-free strategy might be applied to detect the length of other neurodegenerative repeat sequences using short probes with a few complementary repeats

Hand-Fabricated CNT/AgNPs Electrodes using Wax-on-Plastic Platforms for Electro-Immunosensing Application

Abstract Fabrication of inexpensive and flexible electronic and electrochemical sensors is in high demand for a wide range of biochemical and biomedical applications. We explore hand fabrication of CNT modified AgNPs electrodes using wax-on-plastic platforms and their application in electrochemical immunosensing. Wax patterns were printed on polyethylene terephthalate-based substrates to laydown templates for the electrodes. Hand painting was employed to fabricate a silver conductive layer using AgNPs ink applied in the hydrophilic regions of the substrate surrounded by wax. CNT was drop cast on top of the working electrodes to improve their electrochemical signal. The device layers were characterized by scanning electron microscopy. The electrochemical performance of the hand fabricated AgNPs and CNT/AgNPs electrodes was tested using cyclic voltammetry, differential pulse voltammetry, and amperometry. The electrochemical response of CNT/AgNPs electrodes was relatively faster, higher, and more selective than unmodified AgNPs sensing electrodes. Finally, the hand-painted CNT/AgNPs electrodes were applied to detect carcinoembryonic antigen (CEA) by measuring the end-product of immunoassay performed on magnetic particles. The detection limit for CEA was found to be 0.46 ng/mL