SERS-based pH-Dependent detection of sulfites in wine by hydrogel nanocomposites

The Reversible and Background-Free Hydrogel-Sensing Platform for Dual-Mode Detection of Acetone in Exhaled Breath

The acetone present in exhaled breath is a promising indicator for diagnosing human health. The fluorescent hydrogel sensor-based portable sensing platform is a highly effective tool for the on-site detection of acetone. However, existing hydrogel sensors are often limited by their irreversibility and autofluorescence. This study constructed an upconversion nanoprobe with reversibility for dual-mode detection of acetone by simply combining upconversion nanoparticles (UCNPs), hydroxylamine sulfate, and thymol blue (TB). The nanoprobe was further embedded into a hydrogel network to construct the background-free hydrogel nanosensor for the portable detection of acetone. The hydrogel nanosensor utilized long-wavelength-excited UCNPs to avoid self-luminescence interference. Hydroxylamine sulfate, as a specific recognition unit, reacted with acetone to induce the protonation of TB, resulting in an increase in absorbance at 548 nm and a decrease in luminescence at 540 nm, enabling visual colorimetric and precise luminescent detection of acetone. Moreover, the hydrogel nanosensor could be restored to its initial state through the deprotonation of TB, thereby achieving reversible detection. Additionally, 3D printing technology was utilized to construct a portable sensing platform for real-time acetone monitoring. The proposed upconversion hydrogel nanosensor in this study paves a new way for developing hydrogel sensors with high sensitivity and reversibility.

Rapid Colorimetric Detection of Sulfite in Red Wine Using Alginate-Copper Laccase Nanozyme with Smartphone as an Optical Readout

Compared with the conventional analytical methods, nanozyme-based colorimetric sensors offer simpler and more accessible solutions for point-of-need food safety monitoring. Herein, Alginate-Cu (AlgCu) is reported as a robust laccase mimetic nanozyme for the colorimetric detection of sulfite in red wine, a common preservative in winemaking. AlgCu represents a rational design of nanozymes where the multifunctional group alginate is used as a coordination environment for the Cu catalytic center, mimicking the amino acids microenvironment in the natural laccase. The laccase activity of the AlgCu is evaluated using 2,4-dichlorophenol as a model substrate, where its oxidized product reacts with 4-aminoantipyrine, forming a reddish-pink compound with an absorption peak at 510 nm. The result showed that the AlgCu exhibited 32.81% higher laccase activity than pristine copper NPs, highlighting the role of a coordination environment in improving catalytic activity. The addition of sulfite decreased the intensity of the catalytic chromogenic product, confirming that sulfite inhibited the laccase mimetic activity of AlgCu. The observed inhibition is linearly related to the sulfite concentration from 2 to 100 μM (R 2 = 0.996), enabling the detection of sulfite down to 0.78 μM. Furthermore, a sulfite concentration down to 4.9 μM could be detected by integrating the colorimetric assay with smartphone color readouts. Analysis of sulfite-spiked red wine samples gave recoveries between 96 and 106%. Overall, the obtained analytical figures of merits signify AlgCu as a robust nanozyme-based colorimetric chemosensor suitable for a point-of-need application in wine quality control and food safety monitoring in general.

Simple and rapid multicolor sensor for seminal plasma ROS detection based on synergistic catalytic etching of gold nanobipyramids dopped agarose composite gel

Excessive reactive oxygen species (ROS) in seminal plasma can trigger male infertility. Therefore, the development of simple and rapid ROS detection methods is urgently needed, particularly for the early self-screening of preconception couples. Herein, a gold nanobipyramid (Au NBP)-based colorimetric hydrogel for convenient and fast ROS detection is described. In the hydrogel, Au NBP is etched efficiently by ROS under the synergistic effect of Fe2+and I-, which finally causes color variations. Besides, agarose gel with the function of molecular sieve enables the separation of biomacromolecules, improving the interference resistance of the system and the stability of Au NBP. This chemical sensor can complete all the tests within 20 min, covering two detection range of 10-125 μM at relative low H2O2 concentration and 125-1000 μM at relative high H2O2 concentration, with the detection limits of 1.76 μM and 12.10 μM (S/N = 3) respectively. Furthermore, via visual observation of the color variations, it allows the initial interpretation of ROS concentration without any additional equipment. We applied this device to the detection of ROS in clinical seminal plasma samples and obtained promising results, demonstrating its potential for rapid and convenient detection in clinical applications.

"Partner" cellulose gel with "dialysis" function: Achieve the integration of filtration-enrichment-SERS detection

Hydrogel and aerogel materials have garnered significant attention in constructing effective surface-enhanced Raman spectroscopy (SERS) substrates due to their excellent adsorption capabilities, high specific surface area, and abundant chemical groups. However, in liquids with complex compositions, non-specific adsorption of macromolecules can lead to surface scaling and pore clogging of the substrate material, limiting the selective enrichment and SERS detection of target molecules. To address this, an innovative aerogel-chimeric hydrogel material (CH@S-CNF/SA/Ag NPs) was developed. The aerogel component, with its high specific surface area and electronegative properties, functions as a SERS "chip" for adsorption and detection of target molecules. Simultaneously, the mesoporous structure of the hydrogel "shell" effectively filters macromolecules from the solution. These CH@S-CNF/SA/Ag NPs were utilized as SERS substrate materials for detecting urine from healthy individuals and patients with chronic kidney disease stage 5 (CKD5). When combined with machine learning algorithms, the detection accuracy reached 99.50%. This work represents a significant advancement in the specific adsorption and SERS detection of small molecules in complex biological samples such as urine and blood.

Protocol for synthesis of spherical silver nanoparticles with stable optical properties and characterization by transmission electron microscopy

The synthesis of metallic plasmonic nanoparticles (NPs) faces challenges in stability and reproducibility, especially with silver. Here, we present a protocol for tunable synthesis of spherical silver NPs (AgNPs) with stable optical properties. We describe steps for preparing solutions, morphological characterization of AgNPs by transmission electron microscopy, and testing stability. AgNPs exhibit enduring stability and compatibility with various pH values. Moreover, they can be functionalized for optical biosensing applications, offering versatility in nanomaterial applications.

Effect of the molecular weight on the sensing mechanism in polyethylene glycol diacrylate/gold nanocomposite optical transducers

The combination of plasmonic nanoparticles and hydrogels results in nanocomposite materials with unprecedented properties that give rise to powerful platforms for optical biosensing. Herein, we propose a physicochemical characterization of plasmonic hydrogel nanocomposites made of polyethylene glycol diacrylate (PEGDA) hydrogels with increasing molecular weights (700-10000 Da) and gold nanoparticles (AuNPs, ∼60 nm). The swelling capability, mechanical properties, and thermal responses of the nanocomposites are analyzed and the combination with the resulting optical properties is elucidated. The different optomechanical properties of the proposed nanocomposites result in different transduction mechanisms, which can be exploited for several biosensing applications. A correlation between the polymer molecular weight, the effective refractive index of the material, and the optical response is found by combining experimental data and numerical simulations. In particular, the localized surface plasmon resonance (LSPR) position of the AuNPs was found to follow a parabolic profile as a function of the monomer molecular weight (MW), while its absorbance intensity was found as inversely proportional to the monomer MW. Low MW PEGDA nanocomposites were found to be responsive to refractive index variations for small molecule sensing. Differently, high MW PEGDA nanocomposites exhibited absorbance intensity increase/decrease as a function of the hydrophobicity/hydrophilicity of the targeted small molecule. The proposed optomechanical model paves the way to the design of innovative platforms for real-life applications, such as wearable sensing, point-of-care testing, and food monitoring via smart packaging devices.