Improvement The Performance Of Smartphone-based Portable Analytical Device For Filed Analysis

Recently,with the rapid improvement in hardware and software,a smartphone is integrated by a mini computer and various sensors,propelling the fields of chemical and biological sensing for broad range of analytes.Based on the considerations in cost and miniaturization,the smartphone-based analytical devices have some shortcomings,such as the non-linear correlation between the brightness of fluorescent image and concentration of luminophore,low sensitivity in colorimetric detections,and baseline drift due to the decay in the intensity of the light source.In this thesis,the performance of the smartphone-based portable fluorescent and colorimetric devices are improved by new design and method.The details are described below.1.Correction the nonlinear relationship between the brightness of fluorescent image and concentration of luminophore in smartphone based device.In a smartphone-based fluorescence detection device,the fluorescence intensity of fluorescent solution is measured by brightness of fluorescence image.Generally,the relationship between the brightness of fluorescence image and fluorescence intensity of fluorescent solution is non-linear,which leads to the non-linear calibration curve.It also reduces the self-calibration efficiency in ratiometric fluorescence method.In this work,we propose a calculation method to linearize the calibration curve.By using the corrected brightness of fluorescent image,the linear range of calibration curve is greatly expanded.Ratiometric fluorescence can eliminate the influence of external factors such as intensity fluctuation of excitation light source,adjustment of camera shooting parameters?exposure time,photosensitivity and focal length?,as well as the change in ambient temperature.The reliability and stability of smartphone-based portable fluorescent device is greatly improved.The smartphone-based ratiometric fluorescent device was applied for field analysis of soluble copper in river water samples,which is based on the fluorescence quenching effect of Cu²⁺to N-doped carbon quantum dots.The fluorescent images in the sample and reference areas in a twin cuvette were captured by the camera in a smartphone.Under optimized conditions,the proposed method was applied to detect Cu²⁺in the range from 1 to 200 nM with the detection limit of 0.43 nmol/L.This simple fluorescence device offers the advantages of portability,reliability and accuracy for field analysis.2.Simultaneous determination of Cu²⁺,Hg²⁺,Fe³⁺in water sample by a smartphone-based three-channel portable ratiometric fluorescent deviceCopper and iron are essential elements for organisms.At the appropriate concentration level,copper and iron play an important role in promoting the metabolism of organisms.Lack or excess of copper and iron will cause certain harm to organisms.Mercury is a heavy metal with serious harm to human health.Hence,sensitive determination of Cu²⁺,Hg²⁺,Fe³⁺in environmental samples is a valuable work.Fluorescent method is well known for high sensitivity in the determination of these three metal ions.In this work,three kinds of carbon quantum dots,CDs-_Cu,CDs-_Fe and CDs-_Hg were prepared in the thermal decomposition method by ammonium citrate,citric acid+1,10-phenanthroline,and EDTA+thiourea as initial materials,respectively.The fluorescence of CDs-_Cu,CDs-_Fe and CDs-_Hg were quenched by Cu²⁺,Fe³⁺and Hg²⁺,respectively,which is the base to detect Cu²⁺,Fe³⁺and Hg²⁺.However,the selectivity of these fluorescent probes should be still improved to meet the needs of complex sample analysis,especially in filed analysis.In this work,we designed a three-channel ratiometric fluorescence detection device using the camera in smartphone as the detector.Under the optimized conditions,the limits of detection for Cu²⁺,Hg²⁺and Fe³⁺are0.5,3 and 30 nmol/L,respectively.In the field analysis,the concentration of these three ions in water samples can be determined simultaneously,which can not only improve the time efficiency,but also effectively reduce the interference among them.3.Determination of dissolved oxygen in water samples by a portable colorimetric device using ratiometric fluorescence for absorbance measurementDissolved oxygen in water is one of the cornerstones of water ecosystem.It is the essential substance for aquatic animals to survive.Hence,dissolved oxygen in water is an indicator of the self-purification ability of a water system.Determination of dissolved oxygen in water on site is helpful to monitor the changes of dissolved oxygen in water in real time.It also reduces the determination errors caused by oxygen in air during sample transportation.In work,we have developed a portable colorimetric detection device for dissolved oxygen determination on site.In a specially designed three-channel cuvette,the absorption colorimetric chamber was sandwiched by two fluorescence measuring chambers.Under the illumination of excitation light,the fluorescence intensity in the first and third chambers is proportional to the intensity of incident light and transmitted light of the colorimetric chamber,respectively.The absorbance of the solution in the colorimetric chamber was measured from the fluorescence intensity ratio of the two fluorescent chambers,which is proportional to the concentration of the absorbent species in the colorimetric charmer.Using carbon quantum dots emitting red fluorescence as the luminophore,the absorbance in the ultraviolet and visible regions can be determined by choosing the excitation wavelength similar to the absorption wavelength of the absorbent.Based on iodometry and Mn-EDTA,two colorimetric methods established and applied for the field analysis of dissolved oxygen were in environmental water samples.4.A smartphone-based portable long-path colorimetric device with self-calibration and application in determination of soluble iron in river watersSensitivity and reliability are two key parameters of an analytical instrument or device.Herein,we reported a smartphone-based portable long-path colorimetric device with self-calibration ability.A mini flashlight,optical filter array and illumination sensor in smartphone were serviced as the light source,wavelength selector and detector,respectively.A flow colorimetric tube with an optical path of 20 cm was used to enhance the sensitivity.The self-focusing ability in the round-bottom tube is helpful to simplify device design.By using the light intensity in empty tube or at a non-absorption wavelength as the internal reference,the baseline drift due to light source intensity decay was corrected effectively.The absorbance measured in the proposed device obeys Lambert-Beer law in the range of 0¹.The sensitivity in long-path colorimetric device was one order of magnitude higher than that in spectrophotometer using 1 cm cuvette.As an example of the practicability,the proposed device was applied to determine the total soluble iron in river samples on site.By using1,10-phenanthroline as the chromogenic reagent,the limit of detection was 0.03?M.This simple colorimetric device offers the advantages of portability,sensitivity and reliability for field analysis.