Recyclable nano CeO₂ POD mimic records a K_m reduction (∼30% and ∼19.72% for TMB and H₂O₂, respectively) in 900 seconds at pH 4.5. ATP boosts catalytic feasibility in nano CeO₂ at physiological pH.

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 (R^TEM) 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.

Nanostructured cerium oxide (CNP) was synthesized via co-precipitation and used as a base matrix to construct an enzyme-less electrochemical sensing platform for a non-electroactive analyte (i.e., melamine in the presence of ascorbic acid (AA)). CeO₂ was screen printed (SP) on prefabricated gold electrodes for the indirect detection of melamine. The melamine concentrations varied in the range of 0.01 ppb to 10 ppm with a fixed amount of ascorbic acid (i.e., 50 ppm). Absorption spectra were obtained from 220 to 400 nm for all melamine concentrations. The cyclic voltammogram (CV) for different melamine concentrations was obtained in the applied voltage range of –1 to +1 V. The peak oxidation current reduced as a function of increased melamine concentration in the presence of ascorbic acid, which was supported by absorption studies. The obtained melamine sensitivities were 64.9 and 80.8 μA/ppb/mm², respectively, without and with ascorbic acid. The limits of detection estimated from three times the signal-to-noise ratio were 1.5 × 10^–3 and 2.4 × 10^–3 ppb, which are the lowest values so far reported to the best of our knowledge. The electrochemical impedance study predicted the increase of the charge transfer characteristics in the presence of AA, which comprehensively correlated with the CV data. The developed sensor can be used for the detection of melamine in milk, dairy products, and other food items.

In pursuit of fabricating subtle and functionally regimented nanostructures, offering enhanced electronic, optical, and catalytic performance; doping of transition metal (TM: Fe and Mn) driven implication on the morphological, structural and optical characteristics of Zinc oxide nanostructure were investigated adopting base catalyze hydrothermal route of synthesis. To contribute to the understanding, prepared nanostructures were characterized employing an array of microscopic and spectroscopic procedures. Morphological characteristics from FESEM revealed a substantial decrease in size, owing to incorporation of transition element (TM: Fe and Mn) in ZnO lattice; unveiling restricted agglomeration in doped ZnO nanostructures. EDX evince no impurity in doped ZnO NPs, doping ended into efficient assimilation of Fe³⁺ and Mn²⁺ ions in place of Zn²⁺ ions. X-ray diffraction assures wurtzite structure of doped ZnO, grain size (Debye-Scherrer's) for doped ZnO NPs discloses reduction (Pristine: ∼31 nm; Fe doped ZnO: ∼27 nm and Mn doped ZnO ∼11 nm). Fe at 1% doped ZnO nanostructure exhibits a significant shrinkage in lattice parameters, Zn–O bond length and unit cell volume. In view of peak width as a function 2, estimated lattice strain in Fe at 1% doped ZnO (ε: 4.09 × 10^–3) experience an increase in micro-strain compared to pristine (ε: 1.27 × 10^–3). Furthermore, optical characteristics reveal a lower band gap compared to bulk ZnO in all the samples. Vibrational properties via Raman and FTIR spectroscopies unravel intricacies of dopant induced modes. Studies decipher positive surface charge potential for pristine, Fe and Mn doped ZnO nanostructures in DI, while doped ZnO nanostructures holds a negative zeta value, accounts to the alteration assimilated in culture medium (Luria broth).