Visible diffuse reflectance smartphone spectrometer with high spectral accuracy

[Display omitted] •Novel diffuse reflection spectroscopy to analyze the surface of solid sample.•Eliminates the traditional requirement of light collection, conditioning and converging optics.•Nonlinear wavelength dependent intensity calibration to extract accurate spectral information.•Low-cost (∼ $ 50) and lightweight (∼ 145 gm) device used for the identification food color adulteration. A smartphone-based spectrometer employing principle of diffuse reflection is reported for the surface analysis of solid samples. The instrument utilizes a thin-film grating to diffract incoming light, while a diffuse reflecting surface projects the image of this diffracted light onto the detector plane. The CMOS camera of smartphone camera directly captures the diffusely reflected photons within its limited field-of-view thus eliminating the need for collection, conditioning and converging optics. The optical setup of the instrument provides facility to calibrate the spectral response considering the nonlinear distribution of the wavelength across the diffraction direction. Additional correction in the detector response at different light intensity results a reduced spectral error with a maximum wavelength resolution of δλ=0.08 nm/pixel in the camera within the spectral range Δλ = (400 – 700) nm. As a proof of the concept, the instrument demonstrates successful detection of color pigments in food samples by absorption measurement of the samples at an average spectral error