Perspectives of characterization and bioconjugation of gold nanoparticles and their application in lateral flow immunosensing

Gold nanoparticles (AuNPs) are an important component in the field of biomedical diagnostics. Because of its unique physicochemical properties, AuNPs have been widely used in biomedical applications such as photothermal cancer therapy, drug delivery, optical imaging, labeling, and biosensing. In this review, we have described synthesis and characterization techniques for AuNPs with recent advancements. Characterization of AuNPs has played an important role in directing its application in various fields and elaborated understanding of its functioning. The characterization techniques used for the analysis of AuNPs utilize its intrinsic properties, such as surface plasmon resonance (SPR) and size-dependent shift in absorption. These properties of AuNPs are furthermore used for the characterization of bioconjugated AuNPs. Surface conjugation of the AuNPs with biomolecules is explored widely for its use in numerous biosensing applications. Biosensor-based diagnostic devices use AuNPs conjugated with a sensing probe for the detection of a specific analyte. AuNPs are also commonly used as a colorimetric sensor in various point-of-care diagnostic techniques. Lateral flow immunosensing (LFIS) technique utilizes AuNPs for the rapid and sensitive detection of various analytes. LFIS is a paper-based detection technique, where the sample containing the analyte flows through the membrane, interacts with immobilized counterparts, and produces results using a detection probe. AuNPs are used as color markers in LFIS, and the presence of an analyte is indicated by the appearance of colored lines on the membrane. The color is a result of the accumulation of AuNP complexes containing the analyte and probe. Effect of characterization parameters of AuNPs on the sensitivity of LFIS, advantages, and disadvantages of using AuNPs for LFIS are discussed concerning the recent reports. Recent applications of AuNPs in LFIS development for the detection of various biomarkers are summarized comprehensively in the table. The review may offer significant insight into the utility of AuNPs for application in the LFIS technique for future development. Graphical abstract Schematic representation of the various applications of gold nanoparticles