Lactate biosensing: The emerging point-of-care and personal health monitoring.

Lactate plays a crucial role in the anaerobic metabolic pathway of humans. In situations of oxygen deficit, its production increases; leading to several life-threatening conditions such as hemorrhage, respiratory failure, trauma or ischemia from lactate acidosis. Lactate level detection and point-of-care (POC) monitoring in a fast, accurate and non-invasive manner is ultimately important for many health care applications. Optical and electrochemical techniques are employed in lactate sensing to achieve high sensitivity and selectivity, miniaturization, portability, simplicity, and low cost. To improve the selectivity and sensitivity, two important enzymes, lactate oxidase (LOx) and lactate dehydrogenese (LDH) are employed. Conventional methods for lactate detection are not fast enough to be used in point-of-care or personal health monitoring settings. Moreover, the existing point-of-care lactate sensing tools follow invasive or partially invasive sampling protocols such as finger pricking. In this review, a comprehensive overview of different lactate biosensing devices is presented. Particularly, the state-of-the-art and prospects of wearable, non-invasive lactate sensing from different biofluids are discussed.

Prospects and Challenges of Volatile Organic Compound Sensors in Human Healthcare.

The chemical signatures of volatile organic compounds (VOCs) in humans can be utilized for point-of-care (POC) diagnosis. Apart from toxic exposure studies, VOCs generated in humans can provide insights into one's healthy and diseased metabolic states, acting as a biomarker for identifying numerous diseases noninvasively. VOC sensors and the technology of e-nose have received significant attention for continuous and selective monitoring of various physiological and pathophysiological conditions of an individual. Noninvasive detection of VOCs is achieved from biomatrices of breath, sweat and saliva. Among these, detection from sweat and saliva can be continuous in real-time. The sensing approaches include optical, chemiresistive and electrochemical techniques. This article provides an overview of such techniques. These, however, have limitations of reliability, precision, selectivity, and stability in continuous monitoring. Such limitations are due to lack of sensor stability and complexity of samples in a multivariate environment, which can lead to false readings. To overcome selectivity barriers, sensor arrays enabling multimodal sensing, have been used with pattern recognition techniques. Stability and precision issues have been addressed through advancements in nanotechnology. The use of various forms of nanomaterial not only enhance sensing performance, but also plays a major role in detection on a miniaturized scale. The rapid growth in medical Internet of Things (IoT) and artificial intelligence paves a pathway for improvements in human theranostics.

Recent advances in metamaterial split-ring-resonator circuits as biosensors and therapeutic agents.

Potential applications of thin film metamaterials are diverse and their realization to offer miniaturized waveguides, antennas and shielding patterns are on anvil. These artificially engineered structures can produce astonishing electromagnetic responses because of their constituents being engineered at much smaller dimensions than the wavelength of the incident electromagnetic wave, hence behaving as artificial materials. Such micro-nano dimensions of thin film metamaterial structures can be customized for various applications due to their exclusive responses to not only electromagnetic, but also to acoustic and thermal waves that surpass the natural materials' properties. In this paper, the recent major advancements in the emerging fields of diagnostics (sensors) and therapeutics involving thin film metamaterials have been reviewed and underlined; discussing their edge over conventional counterpart techniques; concentrating on their design considerations and feasible ways of achieving them. Challenges faced in sensitivity, precision, accuracy and factors that interfere with the degree of performance of the sensors are also dealt with, herein.