Smartphone-Based Spectral Analysis Device For Water Quality Testing

Spectral analysis is one of the commonly used methods for detecting the composition and content of substances.Spectral detection can detect the substance composition of the analyte without destroying the sample.It is widely used in biological,chemical,medical,environmental and other fields.Spectrometer is a necessary basic instrument in many materials analysis laboratories.However,the traditional spectrometer has a complex structure,a large volume,and a very high price.Therefore,the research of small,portable spectrometers has become an important development direction in the field of spectral analysis.In recent years,the rapid development and high popularity of smart phones has greatly promoted the development and research of various types of portable application devices and instruments based on smartphones.In addition,spectral analysis technologies have many applications that are closely related to people's lives,such as food safety monitoring,the analysis of pharmaceutical ingredients,environmental pollutants,skin health tests,and so on,and the demand of the market is promoting the continuous emergence of various new types of smartphone sensors products for analysis.Therefore,the development of spectral analysis sensors based on smartphone has broad application prospects,which have many advantages such as smart and portable,compact,highly integrated and responsive.In this paper,the LED flashlight built-in the smartphone was used as the broadband light source,and a spectral analysis device based on smartphone was developed.The polycarbonate layer in ordinary optical disc was used to prepare different periodic micro-nano structures,which was used as diffraction gratings for spectral analysis in this device.The diffraction grating effectively improves the pixel utilization rate of the camera and the wavelength resolution of the device,and also reduces the cost of the device.Then this device was used to achieve quantitative detection of chromium(VI)and nitrite in water.The main contents of this article are as follows:1.A spectral analysis device based on smartphones was built.First,the spectrum images of the samples are captured by a smartphone,then we analyze the spectral image to obtain the corresponding absorption spectrum of the sample,thereby the detection working curve was established.Finally the quantitative detection of the sample to be measured was achieved.In this device,the wavelength and pixel calibration of the instrument was performed by three narrow band filters of different wavelengths.Because of spectral limits of the smartphone's built-in flashlight source and range limitations of rear-lens technology in the CMOS-inducible wavelength,the device can achieve quantitative detection in the visible light range of 450 nm to 650 nm.And its detection sensitivity was basically the same as the results of UV-visible spectrophotometers commonly used in laboratories.2.A low-cost method for the preparation of diffraction gratings for spectral analysis was studied.Based on the periodic micro-nano structure in the polycarbonate layer of a common optical disc and the adhesiveness and shrinkage of polyacrylamide gels,the micro-nano structures in the structural layer of the optical disc are transferred and then diffraction gratings with different periodic structures are prepared.At the same time,the atomic force microscope was used in this paper to characterize the grating structure.3.The developed spectral analysis device was used to quantitatively detect the concentration of hexavalent chromium and nitrite in water.Hexavalent chromium and nitrite are extremely harmful to human health.Therefore,real-time monitoring and quantitative detection of hexavalent chromium and nitrite ions in water are of great significance.Combining with spectrophotometry,we used the developed spectral analysis device to establish the working curve between the concentration and absorbance and finally achieved quantitative detection of hexavalent chromium and nitrite in water,and the detection limit meets the requirements of national standards.