Continuous glucose monitors are crucial for diabetes management, but invasive sampling, signal drift and frequent calibrations restrict their widespread usage. Microneedle sensors are emerging as a minimally-invasive platform for real-time monitoring of clinical parameters in interstitial fluid. Herein, a painless and flexible microneedle sensing patch is constructed by a mechanically-strong microneedle base and a thin layer of fluorescent hydrogel sensor for on-site, accurate, and continuous glucose monitoring. The Förster resonance energy transfer (FRET)-based hydrogel sensors are fabricated by facile photopolymerizations of acryloylated FRET pairs and glucose-specific phenylboronic acid. The optimized hydrogel sensor enables quantification of glucose with reversibility, high selectivity, and signal stability against photobleaching. Poly (ethylene glycol diacrylate)-co-polyacrylamide hydrogel is utilized as the microneedle base, facilitating effective skin piercing and biofluid extraction. The integrated microneedle sensor patch displays a sensitivity of 0.029 mM-1 in the (patho)physiological range, a low detection limit of 0.193 mM, and a response time of 7.7 min in human serum. Hypoglycemia, euglycemia and hyperglycemia are continuously monitored over 6 h simulated meal and rest activities in a porcine skin model. This microneedle sensor with high transdermal analytical performance offers a powerful tool for continuous diabetes monitoring at point-of-care settings.

The co-existence and co-transmission of neuropeptides and small molecule neurotransmitters in the same neuron is a fundamental aspect of almost all neurons across various species. However, the differences regarding their in vivo spatiotemporal dynamics and underlying molecular regulation remain poorly understood. Here, we developed a GPCR-activation-based (GRAB) sensor for detecting short neuropeptide F (sNPF) with high sensitivity and spatiotemporal resolution. Furthermore, we explore the differences of in vivo dynamics and molecular regulation between sNPF and acetylcholine (ACh) from the same neurons. Interestingly, the release of sNPF and ACh shows different spatiotemporal dynamics. Notably, we found that distinct synaptotagmins (Syt) are involved in these two processes, as Syt7 and Sytα for sNPF release, while Syt1 for ACh release. Thus, this new GRAB sensor provides a powerful tool for studying neuropeptide release and providing new insights into the distinct release dynamics and molecular regulation between neuropeptides and small molecule neurotransmitters.

Norepinephrine (NE) is an essential biogenic monoamine neurotransmitter. The first-generation NE sensor makes in vivo, real-time, cell-type-specific and region-specific NE detection possible, but its low NE sensitivity limits its utility. Here, we developed the second-generation GPCR-activation-based NE sensors (GRABNE2m and GRABNE2h) with a superior response and high sensitivity and selectivity to NE both in vitro and in vivo. Notably, these sensors can detect NE release triggered by either optogenetic or behavioral stimuli in freely moving mice, producing robust signals in the locus coeruleus and hypothalamus. With the development of a novel transgenic mouse line, we recorded both NE release and calcium dynamics with dual-color fiber photometry throughout the sleep-wake cycle; moreover, dual-color mesoscopic imaging revealed cell-type-specific spatiotemporal dynamics of NE and calcium during sensory processing and locomotion. Thus, these new GRABNE sensors are valuable tools for monitoring the precise spatiotemporal release of NE in vivo, providing new insights into the physiological and pathophysiological roles of NE.

Interest in the use of sensors based on metal-organic frameworks (MOFs) to detect food pollutants has been growing recently due to the desirable characteristics of MOFs, including uniform structures, large surface area, ultrahigh porosity and easy-to-functionalize surface. Fundamentally, this review offers an excellent solution using MOFs-based sensors (e.g., fluorescent, electrochemical, electrochemiluminescence, surface-enhanced Raman spectroscopy, and colorimetric sensors) to detect food contaminants such as pesticide residues, mycotoxins, antibiotics, food additives, and other hazardous candidates. More importantly, their application scenarios and advantages in food detection are also introduced in more detail. Therefore, this systematic review analyzes detection limits, linear ranges, the role of functionalities, and immobilized nanoparticles utilized in preparing MOFs-based sensors. Additionally, the main limitations of each sensing type, along with the enhancement mechanisms of MOFs in addressing efficient sensing are discussed. Finally, the limitations and potential trends of MOFs-based materials in food contaminant detection are also highlighted.

Ochratoxin A (OTA), a mycotoxin found in various food items, possesses significant health risks due to its carcinogenic and toxic properties. Thus, detecting OTA is crucial to ensure food safety. Among the reported analytical methods, there has yet to be one that achieves fast, selective, and portable detection of OTA. In this study, we explore a novel supramolecular sensor, DOCE@ALB, utilizing human serum albumin as the host and a flavonoid fluorescent indicator as the guest. On the basis of indicator displacement assay, this sensor boasts an ultra-fast response time of just 5 s, high sensitivity with a limit of detection at 0.39 ppb, exceptional selectivity, and a noticeable ratiometric fluorescence response to OTA. This discernible color change and portability of the sensor make it suitable for on-site OTA detection in real food samples, including flour, beer, and wine, simply using a smartphone. In comparison to previously reported methods, our approach has showcased notable advantages in both response time and portability, addressing a critical need for food safety and regulatory compliance.

Biogenic amines (BAs), as important indicators for evaluating food spoilage caused by fermentation processes or microbial activities, present significant risks of food safety. Consequently, the development of a simple, sensitive, and selective detection method for amines is of great importance. In this study, we proposed a three-in-one sensor 3,6-bis(dimethylamino)-9-(ethylthio)xanthylium (PSE) for high sensitivity and selectivity detecting BAs with multimodal responses, including olfactory, colorimetric, and fluorescent signals, thus facilitating convenient real-time detection of BAs. Mechanism study indicated that the nucleophilic substitution of PSE with BAs induced such rapid multi-responses with a low detection limit (LOD = 0.03 μM). We further fabricated PSE loaded paper for portable detection of BAs vapors. And the accurate determination of BAs levels is achieved through analyzing the RGB color mode. Finally, we successfully applied these test strips for non-destructive assessing meat beef freshness with the assistance of a smartphone in on-site scenarios.

The pollution of heavy metals such as Cu2+ is still serious and the discharge of sewage of Cu2+ will cause damage to soil environment and human health. Herein, a biomass-based solid-state fluorescence detection platform (CPU-CDs) was developed as fluorescent sensor for detection Cu2+ via fluorescence and colorimetric dual-model methods in real time. CPU-CDs was composed of xylan-derived CDs (U-CDs) and cotton cellulose paper, which exhibiting good reusability, non-toxicity, excellent fluorescence characteristics and high biocompatibility. Further, CPU-CDs displayed high effectiveness and sensitivity for Cu2+ with the detection limit as low as 0.14 μM, which was well below U.S. EPA safety levels (20 μM). Practical application indicated that CPU-CDs could achieve precision response of Cu2+ change in real environment water samples with good recovery range of 90 %-119 %. This strategy demonstrated a promising biomass solid-state fluorescence sensor for Cu2+ detection for water treatment research, which is of great significance in dealing with water pollution caused by heavy metal ions.

Fluorescent point-of-care (POC) sensors have found great utility in fields like clinical diagnosis, food testing, and environmental monitoring. Herein, we developed a highly stable POC sensor that enabled the visual detection of tetracycline (TC) in a distinct fluorescent-traffic-light manner. In the sensor, a composite material of copper nanoclusters and metal-organic framework (CuNCs@MOF-5) prepared with a facile one-pot synthetic strategy was employed as the core element for target recognition and signal transduction. As evidenced by experiments, the as-prepared CuNCs@MOF-5 exhibited significantly improved fluorescence properties in terms of emission enhancement (about 28-fold) and stability improvement (over 110 days) compared to the CuNCs without confining and protection by MOF-5. More importantly, it was found that TC could uniquely interact with Zn(II) to trigger the disassembly of CuNCs@MOF-5, resulting in green fluorescence emission from the TC-Zn(II) complex and red fluorescence weakening of CuNCs. On the basis of this finding, a simple and stable sensor was proposed for POC detection of TC, which demonstrated high sensitivity, selectivity, and reproducibility. In addition to homogeneous visual detection in a 96-well plate, a CuNCs@MOF-5-contained agarose gel array was easily fabricated to achieve direct detection of TC in milk without any pretreatment, thanks to the size-sieving effect of the gel. Moreover, a test paper array was also put forward for low-cost TC detection, which indicates the extensibility and practicability of this sensing strategy.

Specific identification and monitoring of senescent cells are essential for the in-depth understanding and regulation of senescence-related life processes and diseases. Fluorescent sensors providing real-time and in situ information with spatiotemporal resolution are unparalleled tools and have contributed greatly to this field. This review focuses on the recent progress in fluorescent sensors for molecularly targeted imaging and real-time tracking of cellular senescence. The molecular design, sensing mechanisms, and biological activities of the sensors are discussed. The sensors are categorized by the types of markers and targeting ligands. Accordingly, their molecular recognition and fluorescent performance towards senescence biomarkers are summarized. Finally, the perspective and challenges in this field are discussed, which are expected to assist future design of next-generation sensors for monitoring cellular senescence.

Molecularly imprinted polymers have received wide attention from various fields owing to their pre-designable, recognition ability, and practicality. However, the disadvantages of the traditional embedding method, which include a slow recognition rate, uneven site recognition, low binding capacity, and incomplete template molecule elution, limit the development of molecular imprinting technology. Surface molecular imprinting techniques have been developed to effectively solve these problems, and different materials are used as carriers in the synthesis of molecularly imprinted polymers. Metal-organic frameworks (MOFs) show great potential as carriers. Because of their high porosity and specific surface area, MOFs can provide a large number of active sites for molecular imprinting, which can improve their detection sensitivity. The variable metal centers and organic ligands of MOF materials can also lead to multiple structures and functions. Numerous types of MOF materials have been synthesized, and the properties of these materials can be tailored by adjusting their pore size and introducing functional groups. MOFs and molecular imprinting technology can be combined to take full advantage of the specific adsorption of molecular imprinting technology and the large specific surface area and multiple active sites of MOFs, thereby expanding the application range of the resulting materials. In this paper, five aspects of the concept of MOF functionalization are discussed: introduction of special ligands, regulation of metal central sites, formation of MOF complexes, derivatization of MOFs, and sacrificial MOFs. The applications of MOF-based molecularly imprinted materials in catalysis, sample pretreatment, drug carriers, fluorescence sensors, and electrochemical sensors are also reviewed. Finally, the existing problems and future development of MOF-based molecularly imprinted materials are discussed and prospected.