Laser-inscribed contact lens sensors for the detection of analytes in the tear fluid

Tears exhibit compositional variations as a response to ocular and systemic metabolic conditions, and they can therefore be used for the assessment of physiological health. Here, microfluidic contact lenses were developed as wearable platforms for in situ tear pH, glucose, protein, and nitrite ions sensing. The microfluidic system was inscribed in commercial contact lenses by CO₂ laser ablation. The microchannel consisted on a central ring with four branches, and biosensors were embedded within microcavities located at the branches ends. The device was tested with artificial tears and colorimetric readouts were performed using a smartphone-MATLAB algorithm based on the nearest neighbor model. Sensors responded within a time range of 15 s, and yielded sensitivities of 12.23 nm/pH unit, 1.4 nm/mmol L⁻¹ of glucose, 0.49 nm/g L⁻¹ of proteins, and 0.03 nm/μmol L⁻¹ of nitrites. Contact lens sensing platforms may provide on-eye tears screening with applications in the monitoring of the ocular health both in clinics and at point-of-care settings.