Abstract
The capability of functional logic operations is highly intriguing, but far from being realized owing to limited recognition element (RE) and complex readout signals, which limit their applications. In this contribution, for a visual colorimetric sensor for melamine (MEL) we described the construction of two- and three-input AND logic gate by exploiting the intrinsic peroxidase (POD)-like activity of CeO2 nanorods (NRs) (~23.04% Ce3+ fraction and aspect ratio (RTEM) of 3.85 ± 0.18) as RE at acidic pH (4.5). Further ATP piloted catalytic tuning of POD-like activity in CeO2 NRs employed for a functional logic gate-controlled MEL sensing at neutral pH (7.4). AND logic circuit operated MEL sensing record colorimetric response time of 15 min to produce blue color proportionate to MEL concentration. The fabricated nanozyme (CeO2)-based logic gate sensor probe for MEL at pH 4.5 showed a linear response from 0.004 nM to 1.56 nM with a limit of detection (LOD) of 4 pM; while translation from acidic to neutral pH (at 7.4) sensor exhibited linear response ranging from 0.2 nM to 3.12 nM with a LOD value of 17 pM. Through CeO2 POD-like nanozyme behavior under acidic and neutral pH, the fabricated logic gate sensor showed high affinity for MEL, generating prominent visual output with picomolar sensitivity, good reproducibility, and stability with relative standard deviation (RSD) <1% and 2%, respectively. A feasibility study in real samples (raw milk and milk powder) showed good recoveries with negligible matrix effect, an anti-interference experiment revealed sensor selectivity, highlighting robust sensor practical utility. With the merits of high sensitivity, specificity, low cost, and simplified sample processing, the developed logic-controlled colorimetric MEL sensing platform with appropriate modifications can be recognized as a potent methodology for on-site analysis of various food adulterants and related applications.
Highlights
Introduction distributed under the terms andThe synergy within the mounting field of nanotechnology and material science is revealing innovative feats toward the design and fabrication of nanomaterials exhibiting enzyme-like activity [1]
(~23.04%) and possessing POD-like activity at pH 4.5 and 7.4 [30], we examined the effect of MEL on the kinetics of CeO2 nanozyme catalyzed H2 O2 -mediated TMB oxidation reactions
Captured transmission electron microscopy (TEM) image analyzed for ~50 NRs using ImageJ revealed an aspect ratio (R = length to diameter ratio) of 3.85 ± 0.18, as shown in Figure 1b as inset
Summary
Introduction distributed under the terms andThe synergy within the mounting field of nanotechnology and material science is revealing innovative feats toward the design and fabrication of nanomaterials exhibiting enzyme-like activity (known as nanozymes) [1]. Enzymes demonstrate high substrate specificity and catalytic activity but present certain drawbacks, such as low operation stability, vulnerability under harsh environmental conditions, complicated recovery and recycling procedures, high cost of synthesis and purification, which greatly curtail their practical applications [7]. As a result of such obstacles causing the ineffectiveness of practical application, “nanozymes” have emerged as a promising candidate for artificial enzymes, owing to small size, high surface-to-volume ratio, increased reactivity, enhanced stabilities, and tunable catalytic activities that have garnered ever-growing research attention. There have been very limited reviews that have discussed nanozymes’ primarily POD-like activity-based catalytic potential concentrating on food safety and quality parameters [13,14]
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