Carboxylic acid functionalized GNPs form conjugates with various protein molecules due to the electrostatic attraction between negatively charged carboxylate groups and positively charged amino groups of protein.

Carboxylic acid functionalized, PEG 5000 coated, OD 50, and H₂O dispersed gold nanoparticles can be potentially used in the development of biosensors, cancer-cell imaging, drug delivery, and photothermal therapy.
AuNPs may be used to prepare SARS-CoV-2 conjugate for COVID-19 detection using lateral flow immunoassay technique. It 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.

The carboxylic acid group binds with various proteins and can be used in targeted drug delivery and gene therapy.

Decreases the cytotoxicity and increases efficiency of GNPs in targeted drug delivery. The PEG increases the stability of the nanoparticles and prevents agglomeration.