Electropolymerization of poly(phenol red) on laser-induced graphene electrode enhanced adsorption of zinc for electrochemical detection

We present a highly sensitive and selective electrode of laser-induced graphene modified with poly(phenol red) (P(PhR)@LIG) for measuring zinc nutrition in rice grains using square wave anodic stripping voltammetry (SWASV). The physicochemical properties of P(PhR)@LIG were investigated with scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), Fourier infrared spectroscopy (FT-IR) and Raman spectroscopy. The modified electrode demonstrated an amplified anodic stripping response of Zn2+ due to the electropolymerization of P(PhR), which enhanced analyte adsorption during the accumulation step of SWASV. Under optimized parameters, the developed sensor provided a linear range from 30 to 3000 μg L-1 with a detection limit of 14.5 μg L-1. The proposed electrode demonstrated good reproducibility and good anti-interference properties. The sensor detected zinc nutrition in rice grain samples with good accuracy and the results were consistent with the standard ICP-OES method.

Smart sensory polymer for straightforward Zn(II) detection in pet food samples

We report on an innovative method to measure the Zn(II) concentration in commercial pet food samples, both wet and dry food. It is based on a colorimetric sensory polymer prepared from commercial monomers and 0.5 % of a synthetic monomer having a quinoline sensory core (N-(8-(2-azidoacetamido)quinolin-5-yl)methacrylamide). We obtained the sensory polymer as crosslinked films by thermally initiated bulk radical polymerization of the monomers of 100 μm thickness, which we punched into Ø6 mm sensory discs. The immersion of the discs in water solutions containing Zn(II) turned the fluorescence on, allowing for the titration of this cation using the G parameter of a digital picture taken to the discs. The limits of detection and quantification were 29 and 87 µg/L, respectively. Furthermore, we measured the concentration of Zn(II) even in the presence of other cations, detecting no significant interferences. Thus, in a further step, we obtained the concentration of Zn(II) from 15 commercial pet food samples, ranging from 19 to 198 mg/kg, following a simple extraction procedure and contacting the extractant with our sensory discs. These results were contrasted with that obtained by ICP-MS as a reference method.

"On-off-on" fluorescent system for detection of Zn2+ in biological samples using quantum dots-carbon dots ratiometric nanosensor

In this work, a novel strategy for Zn²⁺ detection was established by using an "on-off-on" ratiometric fluorescent nanosensor with the help of ethylene diaminetetraacetic acid (EDTA), a common metal chelating agent. The simple and practical ratiometric fluorescent nanosensor was synthesized by covalently binding CdTe quantum dots (QDs) and carbon dots (CDs), possessing two emission peaks at 525 nm and 450 nm under a single wavelength excitation of 360 nm, respectively. The CdTe QDs served as the response signal label, and the CDs, having no response to the analytes, acted as the reference signal. The fluorescence emission of the nanosensor was turned off to create a low-level "off" state when EDTA was added, and turned on dramatically with the addition of the target Zn²⁺. Under the optimal conditions, the change of the fluorescence intensity ratio of the nanosensor at 525 nm and 450 nm (ΔF₅₂₅/F₄₅₀) had good linearity against the concentrations of Zn²⁺ within a dynamic linear range of 0.50-40 μM. The limit of detection was as low as 0.33 μM (3σ/K), which was low enough for the detection of Zn²⁺ in human body. The proposed method was successfully applied to the detection of Zn²⁺ in human urine and plasma with RSDs less than 10%. The results show that the as-prepared QDs-CDs ratiometric nanosensor has potential application of clinical detection of Zn²⁺ in the human body.