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Lactate is one of the potential biomarkers for assessing the human condition in clinical medicine or sports application. Lactate measurement could help in alerting various emergency conditions, such as bleeding, hypoxia, respiratory failure, and sepsis. Lactate monitoring could also benefit athletes in monitoring their muscle activity to prevent injury due to excessive muscle use or fatigue. In light of this, biosensor technology has been widely explored, especially on the use of electrochemical sensors to analyze the content of biological samples through direct biological activities conversion to electronic signals. This has become imperative for the detection of lactate which offers easy, quick, and reliable measurement. Despite enzymatic sensors being the focus of many studies, the non-enzymatic sensor has started to gain attention in recent years to overcome the stability issue of enzymes. This review presents an overview of the concepts, applications, and recent advancements of different electrochemical lactate sensors. A comparison of recent studies for both enzymatic and non-enzymatic lactate sensors based on electrode modification, enzymes, enzymes immobilizer, and several performance factors, including sensitivity, linearity, detection limit, and storage stability, all of which have been performed. Towards the end, this review also highlights some recommendations for future development of lactate sensors.

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Sweat analysis offers non-invasive real-time on-body measurement for wearable sensors. However, there are still gaps in current developed sweat-sensing devices (SSDs) regarding the concerns of mixing fresh and old sweat and real-time measurement, which are the requirements to ensure accurate the measurement of wearable devices. This review paper discusses these limitations by aiding model designs, features, performance, and the device operation for exploring the SSDs used in different sweat collection tools, focusing on continuous and non-continuous flow sweat analysis. In addition, the paper also comprehensively presents various sweat biomarkers that have been explored by earlier works in order to broaden the use of non-invasive sweat samples in healthcare and related applications. This work also discusses the target analyte’s response mechanism for different sweat compositions, categories of sweat collection devices, and recent advances in SSDs regarding optimal design, functionality, and performance.

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