Surface-enhanced Raman scattering (SERS)-based pH sensors have been widely applied; However, the used 4-mercaptobenzoic acid (4-MBA) probes exhibit small pH-sensitive peak changes (carboxyl group) and strong susceptibility to interference, leading to inaccurate measurements. To address these limitations, we developed a SERS pH sensor using 2,5-dimercaptoterephthalic acid (2,5-DMTA) as the probe, which contains dual carboxyl groups. These carboxyl groups undergo reversible protonation-deprotonation, producing pronounced and reproducible spectral responses that enhance detection accuracy. The developed sensor enabled reliable detection across the acidic pH range of 0-7, showing good linearity (R2 = 0.9786) and compensating for the weak acidic response of 4-MBA. Importantly, the 2,5-DMTA-based pH sensor demonstrated much better detection accuracy (detection relative standard deviation RSD less than 5%) than the 4-MBA-based SERS pH sensor (detection RSD ≈ 20%). To further improve measurement accuracy in complex matrices, the sensor was embedded in hot agarose to form an AuNP@hydrogel substrate, effectively suppressing interference from small molecules. Moreover, the developed sensor also shows satisfactory online pH monitoring features, including good reversibility (≥6 cycles), high stability of continuous measurements (30 min), and long-term storage stability (30 days). Integrated with a microfluidic 3D-printed flow cell, the system enabled rapid response (∼120 s) and online pH monitoring, and was successfully applied to continuous testing in lake water. Overall, this SERS platform provides a robust and accurate solution for SERS-based pH detection under acidic and complex environmental conditions.

Rapid and robust ppb-level H2S sensing is of great importance for environmental monitoring, industrial safety, food quality control, and disease screening. However, improving the H2S sensing properties of semiconductor oxides under low-power conditions remains a significant challenge. In this work, an acid etching method was utilized to precisely control the elemental distribution in bimetallic nanoalloys. By tailoring the Ni distribution in PdNi alloy nanoparticles anchored on ZnO nanosheets, an ultralow detection limit of 5 ppb for H2S was achieved at a working temperature of 140 °C. More importantly, the sensor also demonstrated fast response and recovery kinetics, with its superior antipoisoning performance attributed to the oxidation of H2S into SO2 instead of sulfates or sulfites, as evidenced by in situ FTIR spectroscopy. Additionally, density functional theory calculations were performed to elucidate the synergistic effect of the PdNi alloy, revealing that Pd atoms act as electron donors while Ni atoms facilitate H2S adsorption. This study provides a viable strategy for optimizing noble metal-modified oxide-based gas sensors.

The calibration of the resonant frequency and Q factor of a quartz tuning fork (QTF) in light-induced thermoelastic spectroscopy (LITES) is essential, but time-consuming and disruptive to ongoing measurements. We report on a beat-frequency (BF) method based on differential-frequency demodulation to achieve precise and real-time calibration of QTF resonant frequency and Q factor while maintaining the full excitation of the QTF in LITES. This distinctive property leads to a double improvement in response amplitude compared to the well-optimized LITES operated with the widely used differential-frequency modulation. The tight locking of a near-infrared laser to a high finesse (∼12000) optical cavity further enhances the laser-gas interaction, and then the system's sensitivity. By targeting the R(4) transition of hydrogen sulfide (H2S), we achieved a minimum detection limit of 157 parts per billion in concentration and a normalized noise equivalent absorption coefficient of 1.25 × 10-12 cm-1·W·Hz-1/2. Comparison with state-of-the-art LITES sensors confirms the superior performance achieved in this work.

Accurate diagnosis of disease is crucial for high-quality healthcare services. Biosensors based on colorimetric signals made efforts to rapidly and accurately analyze clinical biosamples. Herein, a microfluidic chip for multicategory marker diagnostics is presented as a platform for the in situ synthesis of MOF-Assisted Reduced Snowflake-like copper nanoparticles (MARS-Cu). MARS-Cu can be rapidly synthesized in 40 s at room temperature and atmospheric pressure and possesses the property of "reversibility" with valence manipulation. The versatile, rapid (approximately 25 min), and multicategory determination of procalcitonin and ascorbic acid using a MARS-Cu-based sensor in a microfluidic chip has been achieved for the accurate assessment of sepsis. The diagnostic accuracy of sepsis was increased from 84.3% using the procalcitonin indicator to 100% using two clinical indicators. The strategy implements "one-chip operation" and "multi-category analysis" and effectively serves as a robust tool and timely strategy for clinical diagnostics and ensuring public health safety.

Printed potentiometric sensors require reliable solid contacts to provide stable and reproducible ion-selective electrodes. However, hampering fabrications and unfavorable maintenance often hinder their breakthrough on a commercial scale. Herein, we develop a solid-contact calcium-selective screen-printed electrode harnessing straightforward manufacturing based on the combination of carbon black (CB) and poly(3,4-ethylene dioxythiophene) doped with poly(sodium 4-styrenesulfonate) (PEDOT:PSS) as an ion-to-electron transducer. Drop-casting was used to simply deposit the CB layer, while PEDOT:PSS was rapidly electropolymerized (71 s) onto the working electrode to deliver affordable manufacturing of the printed electrode while ensuring valid potentiometric performance. Subsequently, the ion-selective membrane (ISM) and the polyvinyl butyral (PVB)-based reference membrane were, respectively, drop-cast onto the working electrode and reference electrode (RE). Upon the optimization of solid-contact layers, the solid-contact Ca2+-ISEs were investigated by evaluating their potentiometric performance versus a conventional RE. CB/PEDOT:PSS-modified screen-printed electrodes demonstrated a low-frequency capacitance of 55 μF, and an outstanding standard potential interelectrode reproducibility (±1 mV). The combination of both types of ion-to-electron transducers provided calcium detection in the linear range 10-1-10-7 M with a Nernstian sensitivity (28.3 ± 0.3 mV/decade), ensured over 28 days under dry storage. Furthermore, the absence of the water layer effect was also demonstrated. Lastly, the fully printed platform was assembled to achieve a miniaturized and easily field-deployable potentiometric device, consisting of CB/PEDOT:PSS/ISM configuration and PVB-based reference membrane on the working electrode and the RE, respectively. The resulted all-solid-state sensor revealed a Nernstian sensitivity with a 29.0 ± 0.5 mV/decade slope and a stable signal up to 72 h (drift = -0.2 mV/h). Analysis carried out using commercially available bottled water also demonstrated the sensor successful performance in the determination of calcium ion in real samples.

Metasurfaces areemerging as a transformative platform in optics,offering compact and versatile alternatives to bulky traditional components.Here, we present a metasurface-enabled, on-chip surface plasmon resonance(SPR) biosensor that enables label-free biomolecular analysis in aminiaturized, chip-scale format. By integrating flat metaoptics togetherwith semiconductor lasers, a collimated fan of light for angle-resolvedSPR measurements can be emitted directly into a glass substrate, eliminatingthe need for conventional optics. As a proof of concept, we demonstratea bulk refractive index sensitivity of 4.9 × 10–6 RIU, along with multiplexed detection of low-molecular-weight microRNAwith limits of detection of 0.1 nM via direct sensing and 0.02 nMwith antibody amplification. The scalability of metasurface fabrication,coupled with the low cost of semiconductor lasers, suggests this platformcan be readily adapted for diverse sensing modalities and mass manufacture,potentially transforming SPR beyond its conventional, benchtop implementations.

Triethylamine (TEA) is a colorless organic liquid known for its high volatility that poses significant irritation to the human respiratory tract; meanwhile, TEA can be released from decaying fish, which can be monitored by a gas sensor. However, conventional TEA gas sensors typically require high operating temperatures, leading to a substantial energy consumption. To address food safety concerns and promote environmental sustainability, the advancement of a TEA sensor that works at room temperature is urgently needed. In our work, an FeWO4/f-MWCNTs-3 chemoresistive gas sensor was fabricated by the hydrothermal method, integrating FeWO4 with multiwalled carbon nanotubes treated with mixed acids (f-MWCNTs). The sensor demonstrates superior performance, owing to its elevated specific surface area, total pore volume, and synergistic effect of p-p heterojunctions. FeWO4/f-MWCNTs-3 demonstrates excellent reproducibility, moisture resistance, stability, a minimal detection threshold of 1 ppm, and relatively rapid response/recovery times of 15/63 s. It attains a 113% response at 100 ppm of TEA at 25 °C. The applicability of FeWO4/f-MWCNTs-3 for assessing fish freshness via TEA concentration analysis from pomfret fish stored at ambient temperature for 14 days was validated, indicating its significance in fish freshness detection methodologies. Additionally, the gas-sensing mechanism of this sensor was further explored using density functional theory (DFT).

Kawasaki disease (KD) is an acute, systemic vasculitis and the leading cause of acquired heart disease. While KD is easily diagnosed with full clinical symptoms, recognizing incomplete or atypical manifestations is challenging due to a limited understanding of its causes, lack of association with a single pathogen, and symptom overlap with common infantile diseases. As our understanding of biomarkers has progressed, efforts have been made to identify unique biomarker profiles in KD. IP-10, a driving chemokine, induces and maintains inflammation in the body, particularly the heart, influencing cardiac diseases. The heightened immune response during acute KD makes IP-10 a promising diagnostic adjunct and indicator of clinical progression. Given its role in activating and regulating inflammatory and immune responses, we propose interferon-gamma inducible protein 10 (IP-10) as one of these markers. Electrochemical biosensors offer a rapid, portable, and affordable alternative to traditional clinical laboratory standards. We showcase sensitive detection and quantification of IP-10 in plasma using a gold electrode platform functionalized with an antibody. The sensor can detect IP-10 up to 8100 pg/mL using 10 μL of sample with great recovery in spiked samples, with <20% variation between the sensors.

In-sensor computing systems demonstrate significant potential for reducing system complexity and enhancing computational efficiency. However, current methodologies predominantly focus on monitoring and processing instantaneous sensor data, neglecting the crucial temporal aspects of sensor inputs. This limitation is particularly significant in healthcare applications, where the human body often exhibits delayed responses to external stimuli. Herein, we developed a synapse-based in-sensor computing system that comprises three retention-engineered synaptic devices connected in parallel to represent the temporal effects of external stimuli. In a proof-of-concept application, the synapse-based in-sensor computing system accurately evaluated the combined temporal risk of hazardous gases, presenting a novel method for assessing the synergistic hazardousness of multiple gases. The presented retention-engineered synapse-based in-sensor computing system offers an innovative solution to the challenges of traditional in-sensor computing, providing a pathway to reduce system complexity and enhance computational efficiency.

Modulating metal oxide-based gas sensors with light is emerging as an alternative to enhance their sensitivity and selectivity. Plasmonic gas sensors based on excitation of the localized surface plasmon resonance (LSPR) in noble metals have recently shown promising properties. The classic approach of incorporating LSPR in sensors is to measure changes in the optical properties of the plasmonic material that depend on the surrounding local environment, i.e., an optical sensor device. The less common approach is to utilize chemiresistive sensors that consist of a gas-sensitive material (like graphene) decorated with plasmonic nanoparticles and employ solely electrical measurements for sensing data acquisition. This work demonstrates a chemiresistive gas sensor graphene/silicon Schottky junction decorated with palladium nanoparticles (PdNPs) that exhibit LSPR in the UV light range. We demonstrate a method of recording responses of plasmonic gas sensors based only on their DC characteristic measurements, which is simplified compared to optical and spectroscopic methods. Supported by the DC characteristics recorded under different UV wavelengths (255 nm, 275 nm, 355 nm), we show that the highest sensitivity to NO2 and NH3 is obtained for plasmonic resonant wavelength excitation of the PdNPs occurring at about 275 nm. The LSPR-modulated sensor response is nearly 14 times greater for NO2 gas compared to NH3 and exhibits a sensitivity toward NO2 gas with an ultralow detection limit of 4 ppb, thus showing that both the selectivity and sensitivity of plasmonic chemiresistive gas sensors can be significantly enhanced by LSPR-tuned light modulation.