Abstract
Developing point-of-care (PoC) diagnostic platforms for carcinoembryonic antigen detection is essential. However, thefew implementations of transferring the signal amplification strategies in electrochemical sensing on paper-based platforms are not satisfactory in terms of detection limit (LOD). In the quest for pushing down LOD, majority of the research has been targeted towards development of improved nanostructured substrates for entrapping more analyte molecules and augmenting the electron transfer rate to the working electrode. But, such approaches have reached saturation. This paper focuses on enhancing the mass transport of the analyte towards the sensor surface through the application of an electric field, in graphene-ZnO nanorods heterostructure. These hybrid nanostructures have been deposited on flexible polyethylene terephthalate substrates with screen printed electrodes for PoC application. The ZnO nanorods have been functionalized with aptamers and the working sensor has been integrated with smartphone interfaced indigenously developed low cost potentiostat. The performance of the system, requiring only 50 µl analyte has been evaluated using electrochemical impedance spectroscopy and validated against commercially available ELISA kit. Limit of detection of 1 fg/ml in human serum with 6.5% coefficient of variation has been demonstrated, which is more than three orders of magnitude lower than the existing attempts on PoC device.
Highlights
Tumor markers have high practical importance in tumor screening and early diagnosis
The main problem limiting the development of electrochemical sensor is the detection limit which is much higher than the polymerase chain reaction (PCR) or fluorescence measurement[11]
There are few efforts for realizing such signal amplification strategies on paper-based platforms with a view to translate them for PoC applications but the lowest limit of carcinoembryonic antigen (CEA) detection achieved is only in few picograms/ml[13,16,17,18]
Summary
Tumor markers have high practical importance in tumor screening and early diagnosis. In this aspect, carcinoembryonic antigen (CEA), an acidic glycoprotein involved in cell adhesion and expressed during human fetal development is a marker for rectal and other cancers like breast cancer, ovarian cancer, lung cancer and pancreatic cancer[1,2]. The need of complex and expensive instruments along with professional operating limit their wide a pplication[6,7] In this regard, the development of affordable, sensitive and portable biosensors requiring low volume samples, less reagents and enabling rapid detection are of significant interest for disease prognosis and point-of-care testing (POCT) applications. Graphene field effect transistor sensors and ZnO nanostructured based electrochemical sensors on flexible substrates have been demonstrated[25,26] These devices have used either lithographically patterned electrodes or solid electrodes which increase the cost and reduce the portability aspects. Commercially available screen-printed electrodes are modified with reduced graphene oxide by drop casting method This leads to non-uniformity in thickness of the thin film and deposition at a specific location is challenging which eventually results in large sensor to sensor variation[29]. Dielectrophoresis (DEP) is a recommended method since it allows localized controlled deposition, has the ability to be performed at room temperature, requires short time of deposition and has appreciable controllability and uniformity[30]
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