The Marriage of Protein and Lanthanide: Unveiling a Time-Resolved Fluorescence Sensor Array Regulated by pH toward High-Throughput Assay of Metal Ions in Biofluids

Single-Probe-Based Sensor Array for Fingerprint Recognition of Trivalent Metal Ions and Application in Water Identification

Abnormal concentration levels of trivalent metal ions (M3+) might hinder their natural biological activities in physiological processes and cause severe health hazards. Herein, a dual-chromophore probe (RhB-TPE) composed of rhodamine and tetraphenylethene (TPE) units was synthesized and explored for discriminating M3+ ions. It exhibited special aggregation and AIE properties in aqueous media. Its ensemble with anionic surfactant SDBS assemblies (RhB-TPE/SDBS) could be utilized as fluorescent sensors for selective and sensitive detection of M3+ ions such as Fe3+, Al3+, and Cr3+ by illustrating quenched TPE emission and switched-on rhodamine emission. Moreover, the use of SDBS assemblies at two concentrations could provide a single-probe-based sensor array and realize four-signal pattern recognition of different concentrations of the three M3+ ions and identify M3+ mixtures or unknown samples. The cross-reactive fluorescence variation was attributed to the M3+ influence on the FRET process from TPE to open-ring form rhodamine in the two ensemble sensors. With the coexistence of Al3+, the optimized RhB-TPE/SDBS ensemble sensor array was successfully applied to differentiate commercially available brand mineral water and purified water, as well as tap water. The present work provides a novel strategy to generate a single-probe-based sensor array and realizes fingerprint recognition of three trivalent metal ions and efficient discrimination of different types of water. The modulation FRET process of a dual chromophore in different surfactant ensembles inspires the future construction of novel and effective sensing platforms.

Identification of Microorganism in Infected Wounds by Positively Charged Selective Sensor Array and Deep Learning Algorithm

Microorganism are ubiquitous and intimately connected with human health and disease management. The accurate and fast identification of pathogenic microorganisms is especially important for diagnosing infections. Herein, three tetraphenylethylene derivatives (S-TDs: TBN, TPN, and TPI) featuring different cationic groups, charge numbers, emission wavelengths, and hydrophobicities were successfully synthesized. Benefiting from distinct cell wall binding properties, S-TDs were collectively utilized to create a sensor array capable of imaging various microorganisms through their characteristic fluorescent signatures. Furthermore, the interaction mechanism between S-TDs and different microorganisms was explored by calculating the binding energy between S-TDs and cell membrane/wall constituents, including phospholipid bilayer and peptidoglycan. Using a combination of the fluorescence sensor array and a deep learning model of residual network (ResNet), readily differentiation of Gram-negative bacteria (G-), Gram-positive bacteria (G+), fungi, and their mixtures was achieved. Specifically, by extensive training of two ResNet models with large quantities of images data from 14 kinds of microorganism stained with S-TDs, identification of microorganism was achieved at high-level accuracy: over 92.8% for both Gram species and antibiotic-resistant species, with 90.35% accuracy for the detection of mixed microorganism in infected wound. This novel method provides a rapid and accurate method for microbial classification, potentially aiding in the diagnosis and treatment of infectious diseases.

A novel ratiometric sensor for fluorimetric and visual dual-mode detection of Al3+ in environmental water based on the target-regulated formation of Eu MOFs

Herein, a novel ratiometric sensor for fluorimetric and smartphone-assisted visual detection of Al3+ in environmental water was developed based on the target-regulated formation of Eu metal-organic frameworks (Eu MOFs). By employing 2-[4-(2-hydroxyethyl) piperazin-1-yl] ethanesulfonic acid (Hepes), Eu3+ and tetracycline (TC) as raw materials, Eu MOFs with red emission were facilely synthesized through the coordination of Eu3+ with Hepes and TC. However, upon the introduction of Al3+, a higher affinity of TC towards Al3+ resulted in the formation of a TC-Al3+ complex with green fluorescence and inhibited the generation of Eu MOFs. This led to an increase in green fluorescence and a decrease in red fluorescence accompanied by the fluorescence color of the solution changing from red to green under the illumination of the UV lamp. Thus, a ratiometric sensor for fluorimetric and the smartphone-assisted visual detection of Al3+ was established. The ratiometric sensor exhibited high sensitivity for Al3+ detection with a detection limit of 0.14 μM for fluorescence detection and 1.21 μM for visual detection. Additionally, the proposed strategy was successfully applied to detect Al3+ in the environmental water samples with satisfactory results, indicating great application prospects for environmental monitoring.

Dual Optical Response Strategy for the Detection of Cytochrome c Using Highly Luminescent Lanthanide-Based Nanotubular Sensor Arrays

Here, we demonstrate a label-free dual optical response strategy for the detection of cytochrome c (Cyt c) with ultrahigh sensitivity using highly luminescent lanthanides containing inorganic-organic hybrid nanotubular sensor arrays. These sensor arrays are formed by the sequential incorporation of the photosensitizers 2,3-dihydroxynaphthalene (DHN) or 1,10-phenanthroline (Phen), and trivalent lanthanide terbium ions (Tb3+) into sodium lithocholate (NaLC) nanotube templates. Our sensing platform relies on the detection and quantification of Cyt c in solution by providing dual photoluminescence quenching responses from the nanotubular hybrid arrays in the presence of Cyt c. The large quenching of the sensitized Tb3+ emission within the DHN/Phen-Tb3+-NaLC nanotubular sensor arrays caused by the strong binding of the photosensitizers to Cyt c provides an important signal response for the selective detection of Cyt c. This long-lived lanthanide emission response-based sensing strategy can be highly advantageous for the detection of Cyt c in a cellular environment eliminating background fluorescence and scattering signals through time-gated measurements. The DHN containing nanotubular sensor arrays (DHN-NaLC and DHN-Tb3+-NaLC) provide an additional quenching response characterized by a unique spectral valley splitting with quantized quenching dip on the DHN fluorescence emission. This spectral quenching dip resulting from efficient FRET between the protein bound DHN photosensitizer and the heme group of Cyt c serves as an important means for specific detection and quantification of Cyt c in the concentration range of 0-30 μM with a low detection limit of around 20 nM.

Label-free competitive time-resolved fluorescent aptasensor for the detection of Pb2+ using ssDNA-sensitized fluorescence of Tb3+ ions

Lead (Pb2+) is one of the most toxic heavy metals, and its environmental pollution and serious damages is a global concern. Therefore, it is necessary to develop effective sensing methods. This study describes a new strategy for the design of label-free competitive time-resolved fluorescent (TRF) aptasensor for detecting Pb2+ ions. The sensing principle of this aptasensor is the competition between Pb2+ and Tb3+ ions to bind to the guanine/thymine-rich sequence (lead aptamer) and the sensitized luminescence of Tb3+ by this sequence. The developed TRF aptasensor demonstrated a good linear detection range from 2.5 nM to 150 nM and a limit of detection (LOD) of 645 pM. In addition, the proposed TRF aptasensor has a high selectivity towards Pb2+, and it has also been successfully utilized to detect this ion in milk and human serum samples. This TRF aptasensor offers advantages such as short analysis time, simple operation, low cost, being label-free, and surpassing the interference of background fluorescence of biological samples due to its TRF characteristic. In this paper, we propose a Tb3+/guanine/thymine-rich sequence system for designing different aptasensors against diverse targets by applying a proper guanine-rich sequence.

An intelligent "chemical tongue" for high-order monitoring ATP-related physiological phosphates and ATP hydrolysis through diverse transduction principles

For discriminating diverse analytes and monitoring a specific chemical reaction, the emerging multi-channel "chemical nose/tongue" is challenging multi-material "chemical nose/tongue". The former contributes greatly to integrating different transduction principles from a single sensing material, avoiding the need for complex design, high cost, and tedious operation involved with the latter. Therefore, this high-order sensing puts a particular emphasis on the effects of encapsulation. Herein, the plasmonic gold nanoparticles (Au NPs) are encapsulated as a core into the fluorescent guanine monophosphate-Tb3+ infinite coordination polymer nanoparticles (GMP-Tb ICPs) to obtain a core-shell nanocomposite named Au NPs@GMP-Tb ICPs. Hence, a dual-channel "chemical tongue" based on Au NPs@GMP-Tb ICPs is present to realize high-order sensing of adenosine triphosphate (ATP)-related physiological phosphates and the monitoring of ATP hydrolysis. Considering the affinity of Tb3+ towards P-O bonds, four inorganic phosphates and three nucleotide phosphates with different phosphate group numbers and steric hindrance effect directly regulate two stimulus responses (fluorescence intensity and UV-vis absorbance) of Au NPs@GMP-Tb ICPs. Robust statistical methods, such as linear discriminant analysis and hierarchical cluster analysis, are used to recognize each phosphate by the developed sensor array either in the aqueous solution or in complex media such as serum, together with efficiently monitored ATP hydrolysis at different intervals. These findings and blind test clarify that the designed "chemical tongue" guarantees interference resistance and strengthens analytical capacity, together with offering valuable insight into "lab-on-a-nanoparticle" development for monitoring specific chemical reactions.

Time-resolved Fluorescence DNA-based Sensors for Reducing Background Fluorescence of Environment

The fluorescence assay is one of the popular methods that is applied for detection of different targets. However, this method may show low sensitivity and high background in biological samples due to the natural fluorescence of different compounds in complicated samples. In addition, it inevitably affects the detection results accuracy. A fundamental solution to this problem is the use of the time-resolved fluorescence technique (TRF). The main component of this technique is the use of long fluorescence lifetime reagents. In this review, various time-resolved fluorescent reagents such as complexes of lanthanide ions, lanthanide-doped inorganic nanoparticles; Mn-doped ZnS quantum dots (QDs) and pyrene excimer are introduced. Moreover, TRF sensors, especially TRF aptasensors (DNA-based sensors) are discussed. This review will give new ideas for researchers to develop novel high-sensitive TRF sensors that can remove or decrease background fluorescence and use them for the detection of various targets in complicated samples without treatment.

Identification of multi-component metal ion mixtures in complex systems using fluorescence sensor arrays

The growing co-contamination of multiple metal ions seriously influences human health due to their synergistic and additive toxicological effects, whereas the rapid discrimination of multiple heavy metal ions in complex aquatic systems remains a major challenge. Herein, a high- throughput fluorescence sensor array was fabricated based on three gold nanoclusters (GSH-Au NCs, OVA-Au NCs, and BSA-Au NCs) for the direct identification and quantification of seven heavy metal ions (Pb²⁺, Fe³⁺, Cu²⁺, Co²⁺, Ag⁺, Hg²⁺ and As³⁺) from environmental waters without sample pretreatment other than filtration. At the detection system, three gold nanoclusters with various ligands possessed distinct binding capacities against metal ions and induced aggregation-induced fluorescence enhancement and quenching, resulting in a unique pattern of fluorescence variations. Meanwhile, integrated the collected fluorescence fingerprints with linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA), a discrete database was obtained for the accurate recognition and sensitive detection of metal ions. Under the optimized conditions, the limit of detection (LOD) of the proposed fluorescence sensor array for metal ions detection at nM concentration level along with a satisfactory accuracy. Importantly, our study indicated that the fluorescence sensor array could be widely used as a general platform in environmental monitoring against multiple targets at low concentrations.

Recent Progress in Sensor Arrays: From Construction Principles of Sensing Elements to Applications

The traditional sensors are designed based on the "lock-and-key" strategy with high selectivity and specificity for detecting specific analytes, which however are not suitable for detecting multiple analytes simultaneously. With the help of pattern recognition technologies, the sensor arrays excel in distinguishing subtle changes caused by multitarget analytes with similar structures in a complex system. To construct a sensor array, the multiple sensing elements are undoubtedly indispensable units that will selectively interact with targets to generate the unique "fingerprints" based on the distinct responses, enabling the identification among various analytes through pattern recognition methods. This comprehensive review mainly focuses on the construction strategies and principles of sensing elements, as well as the applications of sensor array for identification and detection of target analytes in a wide range of fields. Furthermore, the present challenges and further perspectives of sensor arrays are discussed in detail.

Novel sensor array distinguishes heavy metal ions based on multiple fluorescence channels from dendritic mesoporous silica nanoparticles

In this work, we demonstrated a sensor array with multiple fluorescence channels using dendritic mesoporous silica nanoparticles embedded with three quantum dots for the determination of four heavy metal ions (Hg²⁺, Cu²⁺, Cr³⁺, and Ag⁺). Carboxyl-modified CdTe QDs with three different fluorescence emission wavelengths were loaded onto a dendritic mesoporous supporter by an amidation reaction. The fluorescence sensor array exhibited excellent analytical performance for discrimination and semi-quantification of heavy metal ions from a single test, which simplified detection procedures. The four heavy metal ions exhibited different degrees of quenching of the fluorescence emission intensities of the three quantum dots and resulted in a variant data matrix for linear discriminant analysis. Under optimized conditions, the fluorescence sensor array discriminated the four heavy metal ions in a concentration range of 0.05-5 μmol/L, and semi-quantified Hg²⁺, Cu²⁺, Cr³⁺, and Ag⁺ with a limit of detection of 2.51 nmol/L, 5.15 nmol/L, 3.81 nmol/L, and 5.74 nmol/L, respectively. The fluorescence sensor array integrated the sensing units into a single nanoparticle instead of the complex multiple detection steps used in traditional sensor arrays, providing an alternative strategy for constructing a single-well sensing platform. Furthermore, the fluorescence sensor array showed great practical potential for distinguishing heavy metal ions in raw water and crayfish samples.

Colorimetric Sensor Array for Identification of Proteins and Classification of Metabolic Profiles under Various Osmolyte Conditions

Rapid and efficient detection and identification of proteins hold great promise in medical diagnostics, treatment of different diseases, and proteomics. Here, we present a simple colorimetric sensor array for the differentiation of proteins in various osmolyte solutions. Osmolytes have different influences on the conformation of proteins, which have differential binding to silver nanoparticles, resulting in color changes. The sensor array shows unique color change patterns for each of the 19 proteins, allowing unambiguous identification. Very interestingly, the differentiation of 19 proteins is related to their molecular weight. Moreover, the sensor array can be used to identify protein mixtures, thermal denaturized proteins, and unknown protein samples. Finally, the sensor array can also analyze the plasma or liver samples of the four groups of salt-sensitive rats fed with different diets, indicating that it has the potential for the classification of metabolic profiles.

Random forest algorithm-enhanced dual-emission molecularly imprinted fluorescence sensing method for rapid detection of pretilachlor in fish and water samples

A sensitive and efficient fluorescence sensor based on dual-emission molecularly imprinted polymers (Dual-em-MIPs) was successfully developed using the random forest (RF) machine-learning algorithm for the rapid detection of pretilachlor. SiO₂ coatings on red-emitting CdSe/ZnS quantum dots (r-SiO₂@QDs) as intermediate light-emitting components are non-selective for pretilachlor, whereas molecularly imprinted layers coated with blue-emitting nitrogen-doped graphene quantum dots (N-GQD_S) are selective. Fluorescence images of the Dual-em-MIPs were acquired. The red (R), green (G), and blue (B) color values of the image were analyzed using an RF algorithm, and the classifier was trained using 103 fluorescent images for automatic analyses. Under optimized conditions, an excellent linear relationship between the sensor and pretilachlor was obtained in the range of 0.001-5.0 mg/L (R², 0.9958). Additionally, the satisfactory recoveries of Dual-em-MIPs ranged between 92.2 % and 107.6 % for the real samples, with a relative standard deviation (RSD) under 6.5 %. The satisfactory recoveries of the RF model based on the fluorescence sensor were 84.2-108.2 % with the RSD under 6.4 %. Overall, the proposed fluorescence sensor based on Dual-em-MIPs and machine learning methods was successfully used to determine pretilachlor in the environment and in aquatic products.

pH Programmed Optical Sensor Arrays for Cancer Plasma Straightforward Discrimination Based on Protein-Responsive Patterns

Optical cross-reactive sensor arrays inspired by the mammalian olfactory system that can realize straightforward discrimination of plasma from cancer patients hold great potential for point-of-care diseases diagnostics. Herein, a pH programmed fluorescence sensor array based on protein-responsive patterns was designed for straightforward discrimination of different types of cancer plasma. It is worth noting that plasma discrimination can be realized only by programming one nanomaterial using different pH values, which greatly simplifies the programmable design of the sensor array, making it an important highlight of this work. In addition, the mechanism of the pH programmed fluorescence sensor array for protein responsiveness was systematically investigated through molecular docking simulation, fluorescence resonance energy transfer (FRET), and fluorescence lifetime experiments. Most importantly, not only can the differences between plasma from healthy people and and from patients with different cancer species including gastric cancer, liver cancer, breast cancer, and cervical cancer be discriminated by this pH programmed fluorescence sensor array, but also the blind test of unknown plasma samples can be well identified with 100% accuracy, indicating its promising prospect in clinical application.

A dual-channel visual sensing system for recognition of multiple metal ions

Here, we propose a simple, rapid, and effective colorimetric sensor array for discrimination of metal ions. The sensor array was constructed using two sensing channels, i.e., gold nanoparticles (AuNPs)- Tetramethylbenzidine (TMB)-H₂O₂ and AuNPs-O-phenylenediamine (OPD)-H₂O₂ reaction systems. The presence of metal ions with positive charges would lead to the corresponding surface charge change of negatively charged AuNPs, resulting in diverse catalytic performances of citrate-modified AuNPs, accompanied by a substantial colorimetric performance of oxidation products of TMB and OPD. Employing the diversity of colorimetric responses of metal ions to the two sensing channels, nine metal ions including Cr³⁺, Fe³⁺, Cu²⁺, Co²⁺, Ni²⁺, Pb²⁺, Mg²⁺, K⁺, and Cd²⁺ were well distinguished with a discrimination accuracy of 100% at a concentration as low as 50 nM. Further experiment showed that the sensor array was also capable of discriminating and quantifying metal ions at various concentrations, as well as the identification of metal ion mixtures. The feasibility of the sensor array was also verified by the successful identification of the nine metal ions in river water samples.

Recent Advances in Intrinsically Fluorescent Polydopamine Materials

Fluorescence nanoparticles have gained much attention due to their unique properties in the sensing and imaging fields. Among the very successful candidates are fluorescent polydopamine (FPDA) nanoparticles, attributed to their simplicity in tracing and excellent biocompatibility. This article aims to highlight the recent achievements in FPDA materials, especially on the part of luminescence mechanisms. We focus on the intrinsic fluorescence of PDA and will not discuss fluorescent reaction with a fluorometric reagent or coupling reaction with a fluorophore, which may cause more in vivo interferences. We believe that intrinsic FPDA presents great potential in bioapplications.

Luminescent Lifetime Regulation of Lanthanide-Doped Nanoparticles for Biosensing

Lanthanide-doped nanoparticles possess numerous advantages including tunable luminescence emission, narrow peak width and excellent optical and thermal stability, especially concerning the long lifetime from microseconds to milliseconds. Differing from other shorter-lifetime fluorescent nanomaterials, the long lifetime of lanthanide-doped nanomaterials is independent with background fluorescence interference and biological tissue depth. This review presents the recent advances in approaches to regulating the lifetime and applications of bioimaging and biodetection. We begin with the introduction of the strategies for regulating the lifetime by modulating the core-shell structure, adjusting the concentration of sensitizer and emitter, changing energy transfer channel, establishing a fluorescence resonance energy transfer pathway and changing temperature. We then summarize the applications of these nanoparticles in biosensing, including ion and molecule detecting, DNA and protease detection, cell labeling, organ imaging and thermal and pH sensing. Finally, the prospects and challenges of the lanthanide lifetime regulation for fundamental research and practical applications are also discussed.

Monitoring the Viral Transmission of SARS-CoV-2 in Still Waterbodies Using a Lanthanide-Doped Carbon Nanoparticle-Based Sensor Array

The latest epidemic of extremely infectious coronavirus disease 2019 (COVID-19) has created a significant public health concern. Despite substantial efforts to contain severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) within a specific location, shortcomings in the surveillance of predominantly asymptomatic infections constrain attempts to identify the epidemiological spread of the virus. Continuous surveillance of wastewater streams, including sewage, offers opportunities to track the spread of SARS-CoV-2, which is believed to be found in fecal waste. To demonstrate the feasibility of SARS-CoV-2 detection in wastewater systems, we herein present a novel facilely constructed fluorescence sensing array based on a panel of three different lanthanide-doped carbon nanoparticles (LnCNPs). The differential fluorescence response pattern due to the counterion-ligand interactions allowed us to employ powerful pattern recognition to effectively detect SARS-CoV-2 and differentiate it from other viruses or bacteria. The sensor results were benchmarked to the gold standard RT-qPCR, and the sensor showed excellent sensitivity (1.5 copies/μL) and a short sample-to-results time of 15 min. This differential response of the sensor array was also explained from the differential mode of binding of the LnCNPs with the surface proteins of the studied bacteria and viruses. Therefore, the developed sensor array provides a cost-effective, community diagnostic tool that could be potentially used as a novel epidemiologic surveillance approach to mitigate the spread of COVID-19.

"Turn-Off" Supramolecular Fluorescence Array Sensor for Heavy Metal Ion Identification

A "turn-off" supramolecular fluorescence array sensor based on the host-guest complexes between fluorescence dyes and cucurbit[n]urils for sensing metal ions was developed. Three fluorescent probes (RhB@Q[7], H33342@2Q[7], and BRE@Q[7]) were used as the sensing units to construct a supramolecular fluorescence array sensor. The binding ability of the metal ions and cucurbituril-dye probes varied; therefore, the probes and metal ions produced different fluorescence responses. When combined with linear discriminant analysis (LDA), the qualitative and quantitative detection of seven metal ions was achieved. In analytical samples, the supramolecular fluorescence array sensor recognized and distinguish seven metal ions. These results provided new research ideas for the rapid analysis and real-time monitoring of different heavy metal ions.

Rotating the C-N Bond in a Coumarin-Pyridine-Based Sensor for Pattern Recognition of Versatile Metal Ions

A cross-reactive sensor array is powerful for high-throughput discrimination of various kinds of metal ions. However, the construction of a multicomponent sensor array is always time-consuming and cost-ineffective. Herein, a practical four-component X1-based sensor array (X1SA) was obtained by simply dissolving a single dye molecule X1 in respective solvents such as methanol, ethanol, dimethyl sulfoxide, and acetonitrile. In this design, X1 exhibits strong solvatochromic fluorescence properties via an excited-state intramolecular proton transfer and intramolecular charge transfer combined mechanism. Moreover, rotation of the C-N bond between the pyridine and coumarin units in X1 enabled it to coordinate with metal ions through different binding modes, which acted as an additional dimension of the sensor array. Inspired by this C-N bond rotation strategy, X1SA was determined to be powerful in discriminating 20 kinds of metal ions in both phosphate-buffered saline and 5% serum media in a range of 0.1-100 μM. In addition, the sensor array was also successfully applied in differentiating similar and mixed metal ions such as Fe³⁺/Fe²⁺, Cd²⁺/Hg²⁺, and Sn²⁺/Pb²⁺ in serum samples, which is meaningful for investigating the biological roles of iron and early diagnosis of related metal poisoning accidents.

Fabricating a wettable microwells array onto a nitrogen plasma-treated ITO substrate: high-throughput fluorimetric platform for selective sensing of ammonia in blood using polymer-stabilized NH2-MIL-125

A high-throughput and selective fluorimetric platform has been constructed for the analysis of ammonia in blood by using a polymer-stabilized metal-organic framework (MOF) of porous NH2-MIL-125, which was coated onto a wettable microwells array constructed on an indium tin oxide (ITO) substrate. It was found that the nitrogen plasma treatment for the ITO substrate could create a super-hydrophilic interface that combined with the hydrophobic pattern yielded a wettable microwells array, enabling the condensation-based enrichment of targets from the sample droplets. Moreover, the NH2-MIL-125 MOF encapsulated using polymers could be firmly coated onto the microwells to act as fluorescent probes for sensing NH3 with enhanced responses. In addition, the use of the polymer polyvinyl pyrrolidone could protect and stabilize the crystals of NH2-MIL-125 probe in aqueous media, revealing the improved hydrophilicity and significantly depressed signal background. The as-developed fluorimetric platform, containing a MOF-coated microwells array, can enable the detection of ammonia in blood, with concentrations ranging linearly from 0.10 to 300 μM. More importantly, this plasma treatment-based fabrication route may hold promise for designing different wettable microwells arrays for the high-throughput detection of multiple targets in the fields of biomedical analysis and environmental monitoring.

Carboxymethyl chitosan‒promoted luminescence of lanthanide metallogel and its application in assay of multiple metal ions

In this work, the luminescence of lanthanide supramolecular metallogel formed by the self-assembly of 5,5',5″-(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)triisophthalate (H₆L) and Tb³⁺ was efficiently promoted by carboxymethyl chitosan (CMCS). The total quantum yield of the resultant metallogel (denoted as H₆L/Tb³⁺/CMCS gel) was 9 times higher than the gel without CMCS. The average lifetime of H₆L/Tb³⁺/CMCS gel increased from 0.51 ms to 1.20 ms. More importantly, the aqueous dispersion of H₆L/Tb³⁺/CMCS xerogels showed a stable and pH-dependent luminescence. Based on the selective affinity of CMCS to different metal ions as well as with the aid of principal component analysis, H₆L/Tb³⁺ /CMCS can be used as a sensor array to distinguish 11 metal ions (P < 0.05). This work provides a new strategy for the design and development of bio-based functional luminescent lanthanide supramolecular metallogels.

Metal-Bridged Graphene-Protein Supraparticles for Analog and Digital Nitric Oxide Sensing

Self-limited nanoassemblies, such as supraparticles (SPs), can be made from virtually any nanoscale components, but SPs from nanocarbons including graphene quantum dots (GQDs), are hardly known because of the weak van der Waals attraction between them. Here it is shown that highly uniform SPs from GQDs can be successfully assembled when the components are bridged by Tb3+ ions supplementing van der Waals interactions. Furthermore, they can be coassembled with superoxide dismutase, which also has weak attraction to GQDs. Tight structural integration of multilevel components into SPs enables efficient transfer of excitonic energy from GQDs and protein to Tb3+ . This mechanism is activated when Cu2+ is reduced to Cu1+ by nitric oxide (NO)-an important biomarker for viral pulmonary infections and Alzheimer's disease. Due to multipronged fluorescence enhancement, the limit of NO detection improves 200 times reaching 10 × 10-12 m. Furthermore, the uniform size of SPs enables digitization of the NO detection using the single particle detection format resulting in confident registration of as few as 600 molecules mL-1 . The practicality of the SP-based assay is demonstrated by the successful monitoring of NO in human breath. The biocompatible SPs combining proteins, carbonaceous nanostructures, and ionic components provide a general path for engineering uniquely sensitive assays for noninvasive tracking of infections and other diseases.

Luminescent lanthanide complexes for reactive oxygen species biosensing and possible application in Alzheimer's diseases

Histopathological hallmarks of Alzheimer's disease (AD) are intracellular neurofibrillary tangles and extracellular formation of senile plaques composed of the aggregated amyloid-beta peptide along with metal ions (copper, iron or zinc). In addition, oxidative stress is considered as an important factor in the etiology of AD and a multitude of metalloproteins and transporters is affected, leading to metal ion misregulation. Redox-active metal ions (e.g., copper) can catalyze the production of reactive oxygen species (ROS) in the presence of molecular oxygen and a reductant such as ascorbate. The ROS thus produced, in particular the hydroxyl radical which is the most reactive one, may contribute to oxidative stress conditions. Thus, detecting ROS in vivo or in biological models of AD is of interest for better understanding AD etiology. The use of biocompatible and highly specific and sensitive probes is needed for such a purpose, since ROS are transient species whose steady-state concentrations are very low. Luminescent lanthanide complexes are sensitive probes that can meet these criteria. The present review focuses on the recent advances in the use of luminescent lanthanide complexes for ROS biosensing. It shows why the use of luminescent lanthanide complexes is of particular interest for selectively detecting ROS ( O 2 · - , HO^• , ¹ O₂ , H₂ O₂ , etc.) in biological samples in the µM-nM range. It particularly focuses on the most recent strategies and discusses what could be expected with the use of luminescent lanthanide complexes for better understanding some of the molecular mechanisms underlying the development of Alzheimer's disease.

Lanthanide-functionalized metal-organic frameworks based ratiometric fluorescent sensor array for identification and determination of antibiotics

Antibiotics have made great contributions to the improvement of human health and life quality. However, the current abuse of antibiotics not only has a serious impact on the environment, but also endangers people's health. For this reason, the simultaneous identification and accurate determination of as many antibiotics in the environment, food and organisms as possible is critical. Herein, a ratiometric fluorescent sensor array based on Eu³⁺ and Tb³⁺ co-doped metal-organic frameworks (MOFs) was fabricated. Benefiting from the sensitization of the organic ligands to Eu³⁺ and Tb³⁺, the reaction of MOFs with various antibiotics resulted in different responses to the ratio of fluorescent intensity at 545 nm and 616 nm (F₅₄₅/F₆₁₆). After these responses were differentiated by principal component analysis (PCA), totally eight kinds of 25 antibiotics were well distinguished with the existence of interfering substances. The proposed sensor array exhibited high accuracy (98%) for the identification of 48 unknown samples in water and outstanding quantitative ability for the mixture of antibiotics. Finally, the practicability of the sensor array for the analysis of real samples was proved. In this strategy, we have not only provided an efficient way for the comprehensive identification and determination of antibiotics, but also promised new opportunities for the development of ratiometric signal based sensor array.

Array-Based Discriminative Optical Biosensors for Identifying Multiple Proteins in Aqueous Solution and Biofluids

Identification of proteins is an important issue both in medical research and in clinical practice as a large number of proteins are closely related to various diseases. Optical sensor arrays with recognition ability have been flourished to apply for distinguishing multiple chemically or structurally similar analytes and analyzing unknown or mixed samples. This review gives an overview of the recent development of array-based discriminative optical biosensors for recognizing proteins and their applications in real samples. Based on the number of sensor elements and the complexity of constructing array-based discriminative systems, these biosensors can be divided into three categories, which include multi-element-based sensor arrays, environment-sensitive sensor arrays and multi-wavelength-based single sensing systems. For each strategy, the construction of sensing platform and detection mechanism are particularly introduced. Meanwhile, the differences and connections between different strategies were discussed. An understanding of these aspects may help to facilitate the development of novel discriminative biosensors and expand their application prospects.

Tb(iii)-doped nanosheets as a fluorescent probe for the detection of dipicolinic acid

A new fluorescent probe based on terbium(iii)-doped nanosheets was designed for detecting low-levels of dipicolinic acid (DPA), a biomarker of bacterial spores. The ability to detect ultra-low concentrations of DPA is therefore of great significance. First, Tb(iii)-doped ytterbium hydroxide nanosheets were obtained by mechanical exfoliation from layered rare-earth hydroxide (LRH) materials. The morphology of the as-synthesized nanosheets was studied by transmission electron microscopy and atomic force microscopy. The Tb(iii)-doped nanosheets are demonstrated to be highly sensitive to DPA, which remarkably enhances Tb(iii) luminescence intensities at a wavelength of 544 nm. Furthermore, Tb(iii) emission increases linearly with DPA concentration. Selectivity studies were conducted by adding different competing aromatic ligands to the sensing solution; however, their fluorescence responses were observed to be negligibly small in comparison with that of DPA. Our findings provide a basis for the application of Tb(iii)-doped nanosheets for accurate, sensitive, and selective monitoring of DPA as a biomarker of anthrax.

A single-component yet multifunctional tongue-mimicking sensor array for upconversion fluorescence biosensing

A novel single-component nanoprobe has been created for the pattern recognition of antioxidants in a “turn on” manner by integrating with the prevention of PDA formation with an antioxidant.