Simultaneous Multi-Analyte Sensing Using a 2D Quad-Beam Diffraction Smartphone Imaging Spectrometer

Abstract A multichannel smartphone spectrometer exploiting multiple identical diffraction orders of a customized 2D diffractive element is reported. The instrument utilizes diffraction grating holographic imaging to converge and capture the multiple diffraction orders simultaneously within the limited field-of-view of the smartphone’s camera detector. This eliminates the requirement of convergence optics as used in conventional spectrometer systems. Each diffraction order can be utilized as a single optical channel for spectroscopic analysis. As proof of concept, a customized 2D grating composed of two identical thin-film 1D gratings orthogonally stacked together is utilized to diffract the light rays emanating from a broadband visible source and produce four identical 1st orders dispersive diffraction in two orthogonal axes. The smartphone camera captures the diffraction orders within its solid angle – a quad-channel spectrometer exploiting the 2D properties of a CMOS detector is demonstrated. Mindful of losses, further increases in channel numbers is possible by simply increasing the number of gratings (N) within the stack spatially separated by an angle θ N = 180 ° / N between successive grating axes. The instrument offers an ultra-low-cost, lightweight, high throughput, rugged and small form factor multichannel spectrometer ideal for field use as well as a laboratory benchtop alternative. To evaluate the performance of the instrument, three chemically and biologically significant parameters are measured simultaneously: - (a) iron concentration [Fe], (b) chlorine concentration [Cl], and (c) pH of the drinking water.