Biosensors were first reported by Leland Charles Clark Jr. in 1962, who conceived the idea of demonstrating the components of a biosensor along with a strategy to integrate a bioreceptor with a transducer device [6]. Figure 1 shows three generations of the development of biosensors, while Table 1 summarizes the evolution pathway.

Point-of-care testing provides susceptible and non-invasive devices for detecting various biomarkers such as glucose in biological samples in a continuous, fast, low-cost, and reliable manner. Microfluidics is a form of technology that develops miniaturized biosensors using fluid mechanics. On the other hand, existing commercial devices are large, slow, expensive, and require human intervention. Despite substantial progress in developing microfluidic-based biosensors, which will continue to evolve in tandem with existing or well-established approaches, automating, integrating, and miniaturizing current conventional devices on a single platform is a challenging task. This issue has gained significant attention concerning the production of microfluidic-based small biosensors. Microfluidic devices have the advantages of mobility, operational transparency, controllability, reliability, accuracy, and stability, with a small response volume. Because of the few peripherals required to execute numerous applications, microfluidic-based biosensors fabricated using different techniques enable faster processing and greater efficiency. Figure 7 shows the schematic representation of various microfabrication techniques which are widely used in microfluidic-based biosensor development [100].

Table 5 summarizes the various microfabrication techniques used in the development of miniaturized microfluidic biosensors with different materials/substrates employed in building microfluidic devices, and their advantages and disadvantages.

Biosensors are utilized to increase quality of life in a variety of applications. The quality, safety, and upkeep of food items as well as their processing are difficult in food processing industries, and hence the food sector would benefit from cost-effective technologies for food authentication and monitoring [121,122,123]. Potentiometric alternating biosensing devices are also used to detect the changes in pH caused by ammonia, and have been used to identify E. coli [124]; ingredients were mixed in a sonicator to separate the bacteria from the food [125].

Enzyme-based biosensors are also used in the dairy industry [126]; flow cells have been linked to biosensors based on screen-printed carbon electrodes, and enzymes are encapsulated by the polymer mounted onto the electrodes. Three organophosphate insecticides in milk have thus been quantified using automated flow-based biosensors [127]. Sugar substitutes are one of the most widely used food additives that are related to a number of conditions, including dental cavities, cardiovascular disease, obesity, and type II diabetes. In this case, multichannel biosensors are considered to be effective for merging lipid films via the electrochemical approaches for rapid and sensitive sweetener screening. Here, MATLAB software is used with a spatiotemporal method to evaluate the signals of glucose and sucrose in natural sugars, saccharin, and cyclamate, which represent artificial sweeteners [128].

In the field of medicine, biosensor applications are fast-growing. Glucose biosensors are frequently used in clinical settings to diagnose diabetes mellitus, requiring precise blood glucose control [129]. A lateral flow assay, also known as a rapid test, is a simple device intended to detect the presence of a target substance in a liquid sample without the need for specialized and costly equipment. Around 85% of the large global market for blood glucose biosensors consists of items used at home. In the medical area, biosensors are frequently employed to diagnose infectious diseases such as urinary tract infections (UTIs), pathogen identification, and antibiotic susceptibility [130]. Human interleukin-II has been detected early by using a novel biosensor based on hafnium (IV) oxide (HfO2). For early cytokine detection, recombinant human IL-10 with a monoclonal antibody is used. The interaction between antibodies and antigens has also been studied with fluorescence patterns and electromechanical impedance spectroscopy, while fluorescence patterns have been employed to produce the bio-recognition of protein. Chen et al. [131] used HfO2 as a bio-field-effect transistor with high sensitivity [132].

New revolutionary technologies in nucleic acid molecular imaging and sequencing have enabled advances in plant research [133]. Conventional mass spectroscopy can accurately identify cellular and subcellular localization and metabolite levels using critical data on the dynamics and location of enzymes, although transporters, substrates, and receptors still need advancement. Biosensors can access these data to quantify an active process under physiological circumstances. Strategies to envision actual processes, such as changing one metabolite into another or generating signal events, have also been attempted [133]. Tsien [134] was the first to produce protein prototype sensors for detecting caspase activity and calcium levels in living cells. These sensors were made using fluorescence resonance energy transfer (FRET) from green fluorescent protein (GFP) spectrum variants. The in vivo detection of calcium oscillations with a high temporal resolution was achieved by the use of a chameleon sensor [135].

In the case of a biological agent, biosensors can be employed for military purposes. Here, the primary goal is to promptly and correctly identify biowarfare agents (BWAs), including bacteria (vegetative and spores), poisons, and viruses. Several attempts have been made to use molecular techniques to build biosensors that can recognize the chemical markers of BWAs. Furthermore, the human papillomavirus (HPV) is a DNA virus with two strands that have been related to aggressive cervical cancer. HPV is divided into two types: HPV 16 and HPV 18 [136,137].