Positively Charged Gold Quantum Dots: An Nanozymatic “Off-On” Sensor for Thiocyanate Detection

Abstract

The concentration of thiocyanate (SCN-) in bodily fluids is a good indicator of potential and severe health issues such as nasal bleeding, goiters, vertigo, unconsciousness, several inflammatory diseases, and cystic fibrosis. Herein, a visual SCN- sensing method has been developed using the enzyme-like nature of positively charged gold quantum dots (Au QDs) mixed with 3,3′,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2). This research also reports a new method of synthesizing positively charged Au QDs directly from gold nanoparticles through a hydrothermal process. Microscopic imaging has showed that the Au QDs were 3–5 nm in size, and the emission wavelength was at 438 nm. Au QDs did not display any enzyme-like nature while mixed up with TMB and H2O2. However, the nanozymatic activity of Au QDs appeared when SCN- was included, leading to a very low detection limit (LOD) of 8 nM and 99–105% recovery in complex media. The steady-state kinetic reaction of Au QDs showed that Au QDs had a lower Michaelis–Menten constant (Km) toward H2O2 and TMB, which indicates that the Au QDs had a higher affinity for H2O2 and TMB than horseradish peroxidase (HRP). A mechanism study has revealed that the scavenging ability of hydroxyl (•OH) radicals by the SCN- group plays an important role in enhancing the sensitivity in this study. The proposed nanozymatic “Off–On” SCN- sensor was also successfully validated in commercial milk samples.

Borophene Quantum Dots with Enhanced Nanozymatic Activity for the Detection of H2O2 and Cardiac Biomarkers

“…The research and discovery of nanomaterials with enzyme-like activity (nanozymes) have been receiving a lot of focus among researchers because of their higher stability and greater cost efficiency. − The innovation of the peroxidase-like activity of iron oxide nanoparticles (Fe 3 O 4 NPs) has inspired many researchers to develop nanomaterials-based artificial enzymes . To date, a large number of nanomaterials have been identified as nanozymes, for example, palladium nanoparticles (Pd NPs), gold nanoparticles (Au NPs), platinum nanoparticles (Pt NPs), graphene, carbon nanotubes and many more nanomaterials .…”

Graphdiyne Quantum Dots for H2O2 and Dopamine Detection

“…The thiocyanate group scavenged the radical, allowed most of the oxidation reaction to happen at the surface of GDY QDs, and oxidized TMB through several oxidation reactions (Scheme ). Ultimately, the radical scavenging activity of the thiocyanate group played a vital role in boosting the nanozymatic activity by originating the radical chain reaction and TMB oxidation. , To confirm the • OH radical formation and scavenging nature of thiocyanate-capped GYD QDs, the TA and DPPH test was performed. As shown in Figure S5A, a strong fluorescence peak (415 nm) with thiocyanate-capped GYD QDs appeared, confirming the formation of the • OH radical in the reaction media that reacted with TA and formed the fluorescent product 2-hydroxy TA.…”

Carbon Dot Biopolymer-Based Flexible Functional Films for Antioxidant and Food Monitoring Applications

“…The free radical scavenging activities of different concentrations of CPCDs were evaluated by DPPH. 71 In brief, different concentrations (7,15,31,62,125,250, and 500 μg/mL) of CPCDs (210 μL) were added to 100 μM methanolic solution of DPPH (1 mL). The mixtures were incubated for 30 min in the dark.…”

“…Nowadays, nanomaterials, such as quantum dots (QDs), which exhibit intriguing electrical and optical properties are gaining much attention. − QDs are nanometer-sized semiconductor crystals made of elements from groups II to VI or III to V. Particles with sizes smaller than the exciton Bohr radius are called QDs . There are many other types of QDs including silicon QDs, , carbon QDs, − graphene QDs, , graphitic carbon nitride QDs, , magnetic QDs , and so forth.…”