Noninvasive Point-of-Care Nanobiosensing of Cervical Cancer as an Auxiliary to Pap-Smear Test

A potential cancer antigen (Ag), protein-phosphatase-1-gamma-2 (PP1γ2), with a restricted expression in testis and sperms has been identified as a biomarker specific to cervical cancer (CaCx). Detection of this cancer biomarker antigen (NCB-Ag) in human urine opens up the possibility of noninvasive detection of CaCx to supplement the dreaded and invasive Pap-smear test. A colorimetric response of an assembly of gold nanoparticles (Au NPs) has been employed for the quantitative, noninvasive, and point-of-care-testing of CaCx in the urine. In order to fabricate the immunosensor, Au NPs of sizes ∼5-20 nm have been chemically modified with a linker, 3,3'-di-thio-di-propionic-acid-di(n-hydroxy-succinimide-ester) (DTSP) to attach the antibody (Ab) specific to the NCB-Ag. Interestingly, the addition of Ag to the composite of Ab-DTSP-Au NPs leads to a significant hypsochromic shift due to a localized surface plasmon resonance phenomenon, which originates from the specific epitope-paratope interaction between the NCB-Ag and Ab-DTSP-Au NPs. The variations in the absorbance and wavelength shift during such attachments of different concentrations of NCB-Ag on the Ab-DTSP-Au NPs composite have been employed as a calibration to identify NCB-Ag in human urine. An in-house prototype has been assembled by integrating a light-emitting diode of a narrow range wavelength in one side of a cuvette in which the reaction has been performed while a sensitive photodetector to the other side to transduce the transmitted signal associated with the loading of NCB-Ag in the Ab-DTSP-Au NPs composite. The proposed immunosensing platform has been tested against other standard proteins to ensure noninterference alongside proving the proof-for-specificity of the NCB detection.