Recent advances in the field of microneedle devices are having an impact on both diagnostic and therapeutic approaches to sustaining healthy populations globally. Whether this is for improving drug and vaccine efficacy or for continuous sensing of key molecular indicators, the past five years have seen increased activity in both the academic and commercial sectors. In this Perspective, we focus on solid microneedle biosensors and discuss the advantages of these devices over alternative clinical diagnostic platforms as well as the technical challenges presented. We will emphasize how their use in continuous measurement of molecules in vivo is made possible with a minimally invasive technique that is simple to perform. This Perspective describes the function and current state of microneedle sensor arrays for the in vivo measurement of both endogenous molecules such as glucose and lactate and drugs such as penicillin.

Objectives: Validation and testing of a microneedle device capable of continuously monitoring lactate concentrations in healthy pregnant volunteers. Setting: Clinical research facility in a Liverpool hospital in the UK. Participants: Seven healthy pregnant women over 18 years old, with no previously diagnosed medical conditions and no reported pregnancy complications, were able to exercise gently for 30 min and do similar exercise routinely. Results: A healthy volunteer proof-of-concept study was carried out measuring lactate continuously during a period of rest and gentle exercise in pregnant women. Women wore a microneedle device during 30 min of gentle exercise in order to monitor their interstitial lactate levels continuously along with having blood draws at regular intervals. Participants completed a questionnaire about their experience (average pain score 0.43/10, average discomfort score 0.14/10). Interstitial lactate mirrored trends in venous lactate in response to exercise. Conclusions: In maternity care, lactate levels are used to support decision-making, especially around evolving sepsis during labour or post-partum haemorrhage management. Little is known about lactate levels during labour; they are presumed to rise due to anaerobic respiration brought about by physical exertion. However, whether in labour or not, if lactate levels rise above 2 mM intervention is triggered in the form of broad-spectrum antibiotics for treatment or prevention of sepsis. Lactate concentration provides a snapshot of a woman’s current clinical condition, which may alter rapidly. The device has possible application during labour and childbirth, where it could have a significant impact by triggering timely interventions while reducing exposure to unnecessary antibiotics. Trial registration number: West of Scotland Research Ethics Committee 4 and prospectively registered ( ISRCTN38095366 ).

Introduction Determination of blood lactate levels supports decision-making in a range of medical conditions. Invasive blood-sampling and laboratory access are often required, and measurements provide a static profile at each instance. We conducted a Phase I clinical study validating performance of a microneedle patch for minimally-invasive, continuous lactate measurement in healthy volunteers. Methods Five healthy adult participants wore a solid microneedle biosensor on their forearms and undertook aerobic exercise for 30 minutes. The microneedle biosensor quantifies lactate concentrations in interstitial fluid (ISF) within the dermis continuously and in real-time. Outputs were captured as sensor current and compared with lactate concentrations from venous blood and microdialysis. Results The biosensor was well-tolerated. Participants generated a median peak venous lactate of 9.25 mmol/L (Interquartile range, 6.73 to 10.71). Microdialysate concentrations of lactate closely correlated with blood. Microneedle biosensor current followed venous lactate concentrations and dynamics, with good agreement seen in all participants. There was an estimated lag-time of 5 minutes (IQR -4 to 11 minutes) between microneedle and blood lactate measurements. Conclusion This study provides first-in-human data on use of a minimally-invasive microneedle biosensor for continuous lactate measurement, providing dynamic monitoring. The platform offers distinct advantages to frequent blood sampling in a wide range of clinical settings, especially where access to laboratory services is limited or blood sampling is infeasible.