Tear and Saliva [Glucose Monitoring](/)

Introduction

Tear and saliva glucose monitoring represents a novel approach to non-invasive glucose monitoring, aiming to correlate glucose levels in biofluids with blood glucose [1]. This method has been explored through two primary avenues: tear monitoring and saliva monitoring.

Tear Monitoring

Tear monitoring has primarily focused on the development of smart contact lenses, a concept initially pioneered by Google/Verily and now pursued by Samsung and various academic groups [2]. Another approach involves the use of conjunctival inserts, as seen in the work by NovioSense [3]. These devices utilize advanced technologies such as amperometric enzymatic sensors or photonic crystals to detect glucose levels in tears.

Saliva Monitoring

On the other hand, saliva monitoring utilizes mouthguards or biosensors equipped with Organic Electrochemical Transistors (OECTs) to amplify the weak signals from glucose in saliva [4].

Challenges and Limitations

Despite the promise of these technologies, they face significant physiological hurdles that have hindered their commercialization. The concentration of glucose in tears and saliva is notably low, being 1/10th to 1/100th of that in blood, which demands extreme sensitivity from the detection devices [5]. Additionally, the "washout effect", where irritation causes reflex tearing or salivation that dilutes the sample, leads to unreliable data [6]. Furthermore, the lag time of 10–20 minutes and environmental interference, such as food in the mouth or wind on the eyes, make these methods currently unsuitable for critical insulin dosing [7]. The failure of the Verily/Alcon lens project in 2018 underscores the difficulty in overcoming the poor correlation between tear and blood glucose levels [8].

Conclusion

In conclusion, while tear and saliva glucose monitoring present innovative solutions for non-invasive glucose monitoring, they are fraught with challenges. Overcoming the physiological and technological barriers is crucial for the successful development and commercialization of these methods.