Strategy To Fabricate Naked-Eye Readout Ultrasensitive Plasmonic Nanosensor Based on Enzyme Mimetic Gold Nanoclusters

Abstract

It is broadly interesting but remains a big challenge to explore nanomaterials-based methods to enable naked-eye observation and determination of ultratrace biomarkers and drugs. In this study, we developed a straightforward and extendable plasmonic nanosensor to enable visually quantitative determination of ultratrace target molecules through combining the use of enzyme-mimetic gold nanoclusters (AuNCs). Starting from sandwiched antibody-antigen (i.e., an analyte)-antibody structure, we conjugated AuNCs on the outer layer antibody to catalyze the decomposition of hydrogen peroxide used to reduce HAuCl4 into gold nanopartilces (AuNPs) for naked eye readout. This strategy is in theory applicable to all immunoreactions available and the protocol proposed to attach AuNCs onto an antibody is suitable to all proteins. The applicability of this type of nanosensor was validated by the determination of various ultratrace analytes such as protein avidin, breast cancer antigen, thyroid hormone, and even methamphetamine (MA), giving a naked-eye-readout limit of detection (LOD), down to 1.0 × 10(-20) M protein avidin, 7.52 × 10(-14) U/mL breast cancer antigen 15-3, 2.0 × 10(-15) mg/mL 3,5,3'-L-triiodothyronine and 2.3 × 10(-18) mg/mL MA. This strategy is thus considered an ultrasensitive way to fabricate plasmonic nanosensors, having wide and invaluable application potential in clinical, biological, and environmental studies, and in food quality control.

Nanomaterials-Based Colorimetric Immunoassays

“…Among the big family of gold nanomaterials, gold nanoclusters (AuNCs) consisting of several to tens of atoms also have peroxidase-like activity [40,49]. Chen and co-workers developed a plasmonic immunoassay to enable visually quantitative determination of ultratrace targets using peroxidase-mimetic AuNCs (Figure 1B) [50]. AuNCs conjugated on the outer layer antibody can catalyze the decomposition of H 2 O 2 , thus reducing HAuCl 4 into AuNPs for the colorimetric signal output.…”

“…( B ) Schematic representation of the plasmonic nanosenor, in which the target molecule is anchored to the substrate by capture antibodies and recognized by other antibodies labeled with gold nanoclusters (AuNCs). Reproduced with permission from [50]. Copyright American Chemical Society, 2016.…”

In Situ Growth of Plasmonic Gold Nanoparticles for the Direct and Sensitive Colorimetric Assay of Glucose

“…However, fabricating these Au NPs usually involves strict and complicated experimental procedures that comprise seed formation or functional group modification . Consequently, introduction of the reaction between H 2 O 2 and to the direct colorimetric detection of targets has gained increased attention . Modulating H 2 O 2 concentrations can effectively adjust the resulting reaction and affect colorimetric signal results.…”

“…Modulating H 2 O 2 concentrations can effectively adjust the resulting reaction and affect colorimetric signal results. Thus, applications of enzymes that can modulate the concentrations of H 2 O 2 have gained extensive efforts to develop impressive sensor‐based on variable color or pressure . However, studies on glucose sensing based on in situ formation of Au NPs are lacking.…”

“…We report a simple Au NP‐based colorimetric assay for highly sensitive and selective glucose determination. In this work, glucose was first oxidized by GOD; H 2 O 2 , which is one of the products, is the actual detecting target molecule . Stabilized by trace Tween‐20, HAuCl 4 is reduced by H 2 O 2 with exhibition of varied colors.…”