Smart Hydrogel Gratings for Sensitive, Facile, and Rapid Detection of Ethanol Concentration

Bioinspired Colorimetric Double Inverse Opal Photonic Crystal Indicators for Ethanol Concentration Sensing in Fermentation Engineering

Photonic crystal-based ethanol concentration indicators with rapid response and brilliant structural color output definitely take a place in colorimetric sensors. Here, based on the H-bond-regulated swelling of acrylate shape memory polymers (SMPs) and the solvent-induced structural color change of the double inverse opal photonic crystals (DIOPCs), new-type photonic crystals (PCs) colorimetric indicators were constructed, exhibiting a span of maximum reflection wavelength (λmax) up to ∼166 nm in response to alcohols with concentrations from 0 to 100 vol %. DIOPC indicators (DIOPCIs) show a rapid response to alcohols (<1.5 s) and output different structural colors (covering from blue to red). The colorimetric sensing mechanism includes the solvent-triggered recovery of the inverse opal skeleton, the cosolvency effect and H-bonds induced swelling/shrinkage of the polymer, the phase separation between polystyrene (PS) microsphere and polymer skeleton, and the light diffraction of DIOPCs. While ensuring a larger λmax span by regulating the H-bond interactions in polymer chains through acrylamide (AAm), AAm-modified DIOPCIs are sensitive to some specific ethanol concentrations. The real-time sensing of ethanol concentration during fermentation verified the practicability of DIOPCIs, thus establishing a visual model between structural color and corresponding fermentation kinetics. We envisage that the DIOPCIs will contribute to the intelligentization of the alcoholic fermentation and distillation industry.

Designable Micro-/Nano-Structured Smart Polymeric Materials

Smart polymeric materials with dynamically tunable physico-chemical characteristics in response to changes of environmental stimuli, have received considerable attention in myriad fields. The diverse combination of their micro-/nano-structural and molecular designs creates promising and exciting opportunities for exploiting advanced smart polymeric materials. Engineering micro-/nano-structures into smart polymeric materials with elaborate molecular design enables intricate coordination between their structures and molecular-level response to cooperatively realize smart functions for practical applications. In this review, recent progresses of smart polymeric materials that combine micro-/nano-structures and molecular design to achieve designed advanced functions are highlighted. Smart hydrogels, gating membranes, gratings, milli-particles, micro-particles and microvalves are employed as typical examples to introduce their design and fabrication strategies. Meanwhile, the key roles of interplay between their micro-/nano-structures and responsive properties to realize the desired functions for their applications are emphasized. Finally, perspectives on the current challenges and opportunities of micro-/nano-structured smart polymeric materials for their future development are presented.

Dual-emission carbon dots for sensitive fluorescence detection of metal ions and ethanol in water

Carbon dots (CDs) have been widely used in biomedical fields because of their superior optical properties, high sensitivity and high selectivity to specific substances. However, there are few studies on trace detection of the ethanol content in aqueous solution using CDs. Herein, novel red fluorescent CDs with dual emission are synthesized and show good dispersibility in various solvents and excitation independence of photoluminescence (PL). After investigating the structure and properties of the red CDs, a multifunctional fluorescent nanoprobe based on the red CDs with high-sensitivity detection for dual-ion trace detection of Fe³⁺ and Cu²⁺ can be successfully constructed. The limit of detection of Fe³⁺ and Cu²⁺ can be up to 0.024 μM and 0.036 μM, respectively, which is superior to that in previous reports. Meanwhile, in view of the specific solvent effect on their PL, the red CDs are able to be applied for trace detection of the ethanol content in aqueous solution. The methods of colorimetry and fluorescence spectrometry are utilized to perform the threshold test and high-sensitivity quantitative analysis of the ethanol content in aqueous solution. Based on this, a multifunctional fluorescent nanoprobe based on the dual-emission red CDs can be obtained, which provides a promising way for their applications in detection and sensing fields.

Multiresonant analysis improves the limit of detection of tilted fiber Bragg grating refractometers

A multiresonant approach based on tracking 27 cladding mode resonances of tilted fiber Bragg grating refractometers is shown to improve the limit of detection by a factor of 3 to 4 relative to the conventional approach of tracking the single-most sensitive resonance. Limits of detection below 2 × 10^-5 in index change are achieved for dilutions of ethanol in water in repeated experiments. In all cases, wavelengths are referenced to the core mode resonance which eliminates the effect of small temperature changes during and between experiments.

A novel chemosensor for sensitive and facile detection of strontium ions based on ion-imprinted hydrogels modified with guanosine derivatives

A novel chemosensor is developed for the sensitive and facile detection of trace strontium ions (Sr²⁺) based on the ion-imprinted hydrogels. With Sr²⁺ as the templates, the ion-imprinted hydrogels are synthesized by copolymerizing the ion-responsive units 5'-O-acryloyl-2',3'-O-isopropylidene guanosine (APG) and the thermo-responsive units N-isopropylacrylamide (NIPAM). In the presence of Sr²⁺, APG units can self-assemble to form planar G-quartets via the complexation with Sr²⁺, which are introduced into the gel network during polymerization. Then Sr²⁺ templates can be removed by multiple repeated washing. When re-exposed to Sr²⁺, the relaxed G-quartets can recognize Sr²⁺, leading to the weakening of electrostatic repulsion between the four oxygen atoms in the G-quartets and inducing the shrinkage of the hydrogels. In this work, the Sr²⁺-imprinted chemosensors are designed as the grating systems for detecting trace Sr²⁺. Based on the array of hydrogel strings synthesized on a nano-scale, the smart grating systems thus constructed can convert and amplify the Sr²⁺ concentration signals to the easily-measurable optical signals. With the Sr²⁺-imprinted hydrogel gratings, trace Sr²⁺ (10^-11 M) in an aqueous solution can be detected sensitively. Moreover, the proposed Sr²⁺-imprinted chemosensors can be integrated with other smart systems for developing various detectors with high performance.

Label-free detection of C-Reactive protein using bioresponsive hydrogel-based surface relief diffraction gratings

Responsive hydrogel-based surface relief gratings have demonstrated great performances as transducers in optical sensing. However, novel and smart designs of hydrogels are needed for the appropriate detection of analytes and biomolecules since the existing materials are very limited to specific molecules. In this work, a biosensing system based on surface relief gratings made of bioresponsive hydrogels has been developed. In particular, the hydrogel contains phosphocholine moieties to specifically recognize C-Reactive protein (CRP). The CRP-Sensing hydrogel capacity to selectively detect CRP was fully demonstrated. Using Direct Laser Interference Patterning, micro-gratings were created on CRP-Sensing hydrogel substrates and applied for the label-free sensing of CRP using a simple laser-based homemade optical setup. Limits of detection (LOD) and quantification (LOQ) in human serum dilutions of 1.07 and 8.92 mg L^-1, respectively, were reached. These results demonstrate that the biosensing system allows the selective label-free detection of CRP within concentration ranges around those related to risks of cardiovascular diseases and sepsis. Besides, amplification strategies have been carried out improving the sensitivity, widening the linear range, and reaching better LOD and LOQ (0.30 mg L^-1 and 4.36 mg L^-1). Finally, all the approaches were tested for the quantification of CRP in certified human serum with recoveries of around 100%.

Hydrogel-based holographic sensors and biosensors: past, present, and future

Hydrogel-based holographic sensors consist of a holographic pattern in a responsive hydrogel that diffracts light at different wavelengths depending on the dimensions and refractive index changes in the material. The material composition of hydrogels can be designed to be specifically responsive to different stimuli, and thus the diffraction pattern can correlate with the amount of analyte. According to this general principle, different approaches have been implemented to achieve label-free optical sensors and biosensors, with advantages such as easy fabrication or naked-eye detection. A review on the different approaches, sensing materials, measurement principles, and detection setups, and future perspectives is offered.