Gold nanoparticle-based colorimetric methods to determine protein contents in artificial urine using membrane micro-concentrators and mobile phone camera

In this paper, we use an ion-exchange membrane disk to develop miniaturized concentration device, which employs gold nanoparticle (GNP) colorimetric assay to determine human serum albumin content in artificial urine samples. When an external field is applied across cation exchange substrate, the ion depletion appears on the anodic side when the ions are enriched on the cathodic side to fulfill mass conservation and electrical neutrality constrains. In particular when the ion exchange substrates are of round shape, the field lines passing through the membrane disk are focused at the exit pole to further enhance concentration polarization to result in a superconcentraiton spot. GNP colorimetric assays to determine albumin are carried out using the miniaturized concentration chip containing a Nafion cation-exchange membrane disk. Under alkaline condition when GNP solution is spiked with albumins to concentrate using the membrane disk, anionic albumins can prevent the concentrated GNP's from aggregation and the concentrated GNP's remain in red color even in highly salty solutions. On the other hand without efficient protections by absorbed albumins, GNP's aggregate and change color to blue. Using smart phone camera to acquire the concentration images of non-aggregated nanoparticles, one linear correlation is found between the red color intensity and the logarithm values of albumin concentration to quantify albumin amounts. This colorimetric assay is validated to determine the samples of the main urine protein, human serum albumin at the range of clinical significance (0.1-20 mu M) in artificial urine matrix containing creatinine and urine. These results prove the feasibility of using the membrane-based micro-concentration device with mobile phone camera. (C) 2016 Elsevier B.V. All rights reserved.