The influenza virus is classified into four types A, B, C, and D, but type A and B are responsible for major illnesses in people with influenza A being the only virus responsible for flu pandemics due to the presence of two surface proteins called hemagglutinin (H) and neuraminidase (N) on the virus. The two subtypes of influenza A virus, H1N1 and H3N2, have been known to cause many flu pandemics. Both subtypes change genetically and antigenically to produce variants (clades and subclades, also know as groups and subgroups). H3N2 tends to change rapidly, both genetically and antigenically whereas that of H1N1 generally tends to have smaller changes. Influenza A (H3N2) viruses have evolved to form many separate, genetically different clades that continue to co-circulate. Influenza A(H3N2) viruses have caused significant deaths as per WHO report. The review describes methods for detection of influenza A(H3N2) viruses by conventional serological methods as well as the advanced methods of molecular biology and biosensors. All these methods are based on different parameters and have different targets but the goal is to improve specificity and increase sensitivity. Amongst the molecular methods, real-time polymerase chain reaction (RT-PCR) is considered a gold standard test due to its many advantages whereas a number of other molecular methods are time-consuming, complex to perform or lack specificity. The review also considers bio-sensing methods for simple, rapid, highly sensitive, and specific detection of H3N2. The classification and principle of various H3N2 biosensors are also discussed.

Metal nanoparticles (NPs) are described in the nanoscale and made from either pure metals or their compounds such as oxides. Metallic NPs have certain indistinct functional groups due to which these can bind with any type of ligand, antibody and drugs. Organic polymers, which conduct electricity, are called conducting polymers (intrinsically conducting polymers). They behave like semiconductors by exhibiting metallic conductivity. Process-ability is the major advantage of conducting polymers. Nanocomposite is a novel material having nano-fillers scattered in a matrix with morphology and interfacial characteristics of nano-composites including their individual property that influence their characteristics. Conducting polymers and NP composites can enhance the rate of electron transport between the current collector material (electrode) and the electrolyte; therefore they have been employed in the construction of improved electrochemical sensors such as amperometric, catalytic and potentiodynamic affinity sensors.