Silver-enhanced colloidal gold dip strip immunoassay integrated with smartphone-based colorimetry for sensitive detection of cardiac marker troponin I

Abstract

Cardiac troponin I (cTnI) is a specific cardiac biomarker for diagnosis of acute myocardial infarction (AMI). A sensitive and simple point-of-care test (POCT) is still required for early detection of AMI. To address this need, we developed a dip strip assay based on sandwich immunoassay coupled with a silver enhancement system. Pre-incubation and silver enhancement were introduced to the dip strip to increase sensitivity. Due to the catalytic reaction of the silver enhancement solution, the red color of AuNPs changed to dark brown as silver ions precipitated and enlarged the AuNPs. The obtained results were easily seen by the naked eye. For quantitative analysis, the color intensity of the results was analyzed using a smartphone with RGB color picker application. The effects of operating parameters (volume of AuNP-Ab conjugate, volume of sample, incubation time, and analysis time) were investigated and optimized. Under optimal conditions, the limit of detection (LOD) by the naked eye was 0.5 ng/mL. The LOD with silver enhancement was 50-fold lower than without. For quantitative analysis using the smartphone, linearity of detection was observed through the range of 0.5–50 ng/mL (R2 = 0.9952) and the LOD was 0.12 ng/mL. The developed method was successfully applied to detection of cTnI in serum samples, achieving analytical recoveries and %RSD in the ranges of 96.10–119.17% and 2.91–5.13%, respectively. Additionally, this developed assay was not cross reactive with the potentially interfering serum proteins. These results showed the great potential of this dip strip assay as an alternative POCT for detection of serum cTnI.

Optical Nanobiosensor-Based Point-of-Care Testing for Cardiovascular Disease Biomarkers

“…Apilux et al also reported a smartphone-based colorimetric PoCT dip strip for sensitive detection of cTnI. 233 The anti-cTnI@AuNPs sandwich immunoassay binds with silver ion and shows a naked eye color change from red to dark brown because of the precipitation of silver ion. This silver-enhanced colloidal gold dip strip immunoassay obtained a LOD of 0.12 ng/mL and detection for 0.5−50 ng/mL (R 2 = 0.9952).…”

“…Smartphone-based imaging analysis of cTnT was obtained in a wide range of concentrations between 0.01 and 0.8 μg/mL and 6.25–50 μg/mL with LOD of 3.9 × 10 –4 μg/mL. Apilux et al also reported a smartphone-based colorimetric PoCT dip strip for sensitive detection of cTnI . The anti-cTnI@AuNPs sandwich immunoassay binds with silver ion and shows a naked eye color change from red to dark brown because of the precipitation of silver ion.…”

Progress in the Optical Sensing of Cardiac Biomarkers

“…At the same time, disappointingly, there was no evaluation of the stability and reproducibility of the new materials, with very few exceptions. Some lateral flow strips were evaluated and found to be stable for months at either 4 °C [ 110 ] or at room temperature [ 104 ].…”

Post-Assay Chemical Enhancement for Highly Sensitive Lateral Flow Immunoassays: A Critical Review

“…( c ) Use of silver enhancement for LFIA of cardiac troponin I. Concentrations of cardiac troponin I are shown above the test strips (i) before silver enhancement and (ii) after silver enhancement [ 87 ].…”