Continuous Non-Invasive Glucose Monitoring via Contact Lenses: Current Approaches and Future Perspectives

Abstract

Diabetes mellitus (DM) is a chronic disease that must be carefully managed to prevent serious complications such as cardiovascular disease, retinopathy, nephropathy and neuropathy. Self-monitoring of blood glucose is a crucial tool for managing diabetes and, at present, all relevant procedures are invasive while they only provide periodic measurements. The pain and measurement intermittency associated with invasive techniques resulted in the exploration of painless, continuous, and non-invasive techniques of glucose measurement that would facilitate intensive management. The focus of this review paper is the existing solutions for continuous non-invasive glucose monitoring via contact lenses (CLs) and to carry out a detailed, qualitative, and comparative analysis to inform prospective researchers on viable pathways. Direct glucose monitoring via CLs is contingent on the detection of biomarkers present in the lacrimal fluid. In this review, emphasis is given on two types of sensors: a graphene-AgNW hybrid sensor and an amperometric sensor. Both sensors can detect the presence of glucose in the lacrimal fluid by using the enzyme, glucose oxidase. Additionally, this review covers fabrication procedures for CL biosensors. Ever since Google published the first glucose monitoring embedded system on a CL, CL biosensors have been considered state-of-the-art in the medical device research and development industry. The CL not only has to have a sensory system, it must also have an embedded integrated circuit (IC) for readout and wireless communication. Moreover, to retain mobility and ease of use of the CLs used for continuous glucose monitoring, the power supply to the solid-state IC on such CLs must be wireless. Currently, there are four methods of powering CLs: utilizing solar energy, via a biofuel cell, or by inductive or radiofrequency (RF) power. Although, there are many limitations associated with each method, the limitations common to all, are safety restrictions and CL size limitations. Bearing this in mind, RF power has received most of the attention in reported literature, whereas solar power has received the least attention in the literature. CLs seem a very promising target for cutting edge biotechnological applications of diagnostic, prognostic and therapeutic relevance.

Correlations of Salivary and Blood Glucose Levels among Six Saliva Collection Methods

“…Not only does an urgent need exist for a non-invasive glucose monitoring technology so as to make a major improvement in the lives of millions of people around the world living with DM, but also to ease preventive monitoring [ 10 ]. Over the past few decades, the non-invasive monitoring of DM by fluid analysis (as well as other biological fluids such as urine, sweat, and saliva) has attracted worldwide attention [ 11 , 12 , 13 ].…”

Janus Hydrogel Microbeads for Glucose Sensing with pH Calibration

“…Our glucose sensor is expected to be biostable, long lasting [ 9 ] and fully implantable, with the simultaneous multi-sensing of glucose and pH to increase accuracy, showing the potential of being a good alternative to the existing glucose-sensing methods for CGM. In addition to those fluorescent-based sensing methods, recently developed glucose sensors targeting body fluids such as saliva and tear fluids are often integrated with a wearable device [ 22 , 23 , 24 , 25 , 26 ]. Applying our fluorescent hydrogel glucose-sensing microbeads to improved wearable devices for measuring such body fluids could also widen the possibilities of stable and patient-friendly CGMs.…”

Lab‐on‐a‐Contact Lens: Recent Advances and Future Opportunities in Diagnostics and Therapeutics

“…[319,322] In recent years, researchers from different fields have worked to solve these challenges to make the SCL wearable platforms more practical. [184,319,323] In this section, we provide discussions about the applicable powering techniques for SCLs, such as radio-frequency identification, wearable batteries, and solar cells. Moreover, we summarize the advanced wireless data transfer technologies, including optics, remote resonance detection, and custom-built application-specific integrated circuits (ASIC).…”

“…The recent technological advances in wearable bioelectronics have enabled the continuous monitoring of tear glucose levels. [ 184 ] However, the opaque, brittle electric units may interfere with the wearer's vision and trigger eye damage. To address these concerns, Park and co‐workers fully integrated glucose sensors, wireless power transfer circuits, and a signal‐visualizable light‐emitting diode (LED) display into a transparent and flexible CL ( Figure a).…”