Microfluidic Immunosensor for Point-of-Care-Testing of Beta-2-Microglobulin in Tear
Surjendu Maity, Subhradip Ghosh, Tamanna Bhuyan, Dipankar Das, Dipankar Bandyopadhyay
Abstract
Quantification of β-2-microglobulin (B2M) in human tear can help in detecting the onset and growth of the dreaded eye disease diabetic retinopathy (DR) for the patients suffering from diabetes mellitus. In this direction, a biosensor has been developed for the point-of-care (POC) estimation of B2M, suitable for early detection and regular monitoring of DR. The immunosensor is composed of a water-based suspension of gold nanoparticles (AuNPs) coated with anti-β-2-microglobulin (anti-B2M) using a linker, which shows a specific coloration due to the localized surface plasmon resonance (LSPR) of AuNPs, when filled inside a specially designed microfluidic cuvette. The design of the microcuvette enables an efficient mixing of the analyte loaded with B2M (e.g., tear) when dispensed in the colored suspension. Subsequently, this process leads to a specific antigen–antibody reaction followed by a change in the intensity of color due to the agglomeration of AuNPs. Remarkably, the LSPR of AuNPs boosts the Raman signals associated with the antigen linked with the AuNP-linker antibody, which can be employed as a novel sensing strategy for accurate estimation of B2M. As an alternative strategy, variations in the color intensities of the suspensions have been measured by integrating a light source in one side of a cuvette and a light-dependent resistor (LDR) to the other side. The resistance of the LDR varies monotonically with the change in the intensity of the transmitted rays when the B2M loading is varied in the analyte. A calibration obtained from the known samples has been employed to detect the unknown B2M level in tear or urine.