Smartphone-based digital image colorimetry for non-enzymatic detection of glucose using gold nanoparticles

Diabetes mellitus, which is caused by high blood glucose, is increasing from time to time due to an unhealthy modern lifestyle. Diabetes can cause complications in many parts of the body and increase the risk of death. So far, glucose assay often used glucose oxidase (GOx) and horseradish peroxidase (HRP) enzymatic system that requires special treatment and other high-cost resources. Thus, developing a simple non-enzymatic analytical method to determine the glucose content in body fluids is necessary. Here, a novel and straightforward method for glucose sensing was developed based on digital image colorimetry (DIC) combined with smartphone detection. Small amounts (< 1 mM) of gold nanoparticles (AuNPs) which has a violet-blue color were employed as colorimetric biosensors that selectively change their color to violet-red upon the addition of glucose. The addition of glucose concentration is linearly proportional to the light absorbance and blue color intensity. These AuNPs color changes were captured as a digital image using a smartphone which then undergo data processing using an application attached to the smartphone. The accuracy of the proposed DIC-smartphone was tested with standard addition (recovery 99.5-103%) and validated with the UV-vis spectrometer. The method has good selectivity and sensitivity, with a detection limit of 0.043 mu M and a linear range from 0 to 40 mu M (R-2 = 0.9984). The method was successfully applied to quantify the glucose concentration in real samples, i.e., urine samples of normal people and diabetic patients that give satisfactory accuracy (< 3.0%) and precision (< 4.2%).