Carboxylic acid functionalized GNPs forms conjugates with various protein molecules due to the electrostatic attraction between negatively charged carboxylate groups and positively charged amino groups of protein.The carboxylic acid group binds with proteins and is used in targeted drug delivery and gene therapy.Gold nanoparticles 50 nm diameter, carboxylic acid functionalized, PEG 5000 coated, dispersion in H2O can be potentially used in the development of biosensors, cancer-cell imaging, drug delivery, and photothermal therapy.AuNPs may also be used in the immobilization of antibodies to improve the sensitivity of optical fiber sensors for the screening of COVID-19. It can also be deposited on the titanium electrode for the formation of a miniaturized device for the electrochemical detection of DNA hybridization.Functionalized Particles have been extensively used to study cellular uptake of nanoparticles and targeted drug delivery.