A New Portable Platform Based On Target-responsive DNA Hydrogel And Gold Nanorods

Point-of-care testing?POCT?is a new detection method,which can quickly get results on site.Because of intuitive results and no need of expensive equipment,naked-eye detection has become one of the most potential signal output methods for POCT.Due to local surface plasmon resonance?LSPR?,gold nanorods?AuNRs?exhibit orange,gray,green,blue,purple,and other color.Since human eyes are more sensitive to color variations with different spectrum than optical density?such as TMB?,the optical properties of AuNRs have a great advantage in naked-eye detection.Therefore,we developed a portable platform for naked-eye detection based on AuNRs.The key to gold nanorods as chromogenic substrates is the ability to detect different concentrations of targets.We investigated the response of gold nanorods to different concentrations of H2O2,indicating the feasibility of AuNRs for naked-eye detection.Next,a glucose signal can be transformed into an AuNRs signal by means of glucose oxidase?GOx?.In order to extend the application of gold nanorods in POCT,signal transduction was also achieved by cascaded enzymatic reactions between glucoamylase?GA?and glucose oxidase.Moreover,we also investigated the response of gold nanorods to GA,which extended the application of AuNRs in POCT.With the development of POCT,more attention have been paid to the accuracy of POCT and the diversity of targets.Functional DNA-cross-linked DNA hydrogels have become a great platform in POCT due to the advantages of wide targets,high stability,specificity and sensitivity.Therefore,a new POCT method?hydrogel-AuNRs?was developed based on DNA hydrogel encapsulating GA as a target-identified unit and AuNRs as a multicolor substrate.After addition of cocaine,the DNA hydrogel was collapsed,leading to release of GA trapped in the hydrogel.Cocaine signal can be transformed into H2O2 signal by means of cascaded enzymatic reactions between GA and GOx.The produced H2O2 can etch AuNRs along horizontal direction,leading to color change of AuNRs.The color change of AuNRs can be observed by naked eye,allowing sensitive,selective and visual detection of cocaine.After simple precipitation by acetonitrile,cocaine in urine could be detected.Meanwhile,the concentration of cocaine can be quantitated by peak shift of AuNRs with UV-Vis spectrophotometer.In addition,Pb²⁺ can be detected based on Pb1GJresponsive hydrogel as a target-identified unit and AuNRs as a multicolor substrate,which verified the versatility of hydrogel-AuNRs method.After simple filtration,20 nM Pb²⁺ in seawater was detected by naked eye.Compared with standard method of ICP-MS,the hydrogel-AuNRs method showed high accuracy for Pb²⁺ assay.These results display that hydrogel-AuNRs method is a new and universal platform for POCT.