Development and optimisation of a near-infrared spectroscopic system for glucose quantification in aqueous and intralipid-based samples

A non-invasive glucose sensing device could revolutionise diabetes treatment. Near Infrared (NIR) spectroscopy is a promising technology for glucose sensing; however, the design and choice of components for NIR spectroscopy can greatly affect the sensing accuracy. We aimed to develop a NIR absorption spectroscopy system to determine liquid glucose concentrations in the physiological range, by evaluating a range of NIR photodetector components and light sources. Three detection assemblies were tested: (i) a dispersive spectrometer with photodiode array, (ii) a Czerny-Turner monochromator with InGaAs photodiode and (iii) a miniature Fourier Transform Infrared (FTIR) spectrometer. A halogen lamp and NIR globar were trialled as potential light sources. The components were systematically tested by comparing the coefficient of determination and standard error of prediction (SEP) for the same set of aqueous glucose samples through 10 mmol l-1 concentration steps. The Czerny-Turner monochromator with InGaAs photodiode, along with the globar, were identified as the optimal components for the system. A range of concentration steps (1-10 mmol l-1) were scanned to identify the physiologically relevant limit of detection, which was identified as 5 mmol/l for glucose in solution. Spectra were then collected from glucose samples in 10% intralipid suspension in the 10-20 mmol l-1 range and the equivalent concentrations in solution. The SEP was greater for the intralipid samples due to strong scattering. Scattering was dominant above 1300 nm, whilst absorption was dominant below 1300 nm. Although alternative approaches achieve better resolution, our system uses simple and readily-available components and presents a platform for a non-invasive NIR glucose sensing device.