Rare Earth-Carbon Dots Nanocomposite-Modified Glass Nanopipettes: Electro-Optical Detection of Bacterial ppGpp.

As an important alarmone nucleotide, guanosine 3'-diphosphate-5'-diphosphate (ppGpp) can regulate the survival of bacteria under strict environmental conditions. Direct detection of ppGpp in bacteria with high sensitivity and selectivity is crucial for elucidating the role of ppGpp in bacterial stringent response. Herein, the terbium-carbon dots nanocomposite (CDs-Tb) modified glass nanopipet was developed for the recognition of ppGpp. The CDs-Tb in glass nanopipette preserved their fluorescence properties as well as the coordination capacity of Tb3+ toward ppGpp. The addition of ppGpp not only led to the fluorescence response of CDs-Tb but also triggered variations of surface charge inside the glass nanopipet, resulting in the ionic current response. Compared with nucleotides with similar structures, this method displayed good selectivity toward ppGpp. Moreover, the dual signals (fluorescence and ionic current) offered a built-in correction for potential interference. Apart from the high selectivity, the proposed method can determine the concentration of ppGpp from 10-13 to 10-7 M. Taking advantage of the significant analytical performance, we monitored ppGpp in Escherichia coli under different nutritional conditions and studied the relationship between ppGpp and DNA repair, which is helpful for overcoming antibiotic resistance and promoting the development of potential drugs for antibacterial treatment.

Room temperature cost-effective synthesis of carbon quantum dots for fluorescence pattern recognition of metal ions.

Herein, a type of low-consuming carbon quantum dot (CD) has been synthesized at room temperature in just 45 minutes via Schiff base reaction between o-phthalaldehyde (OPA) and polyethyleneimine (PEI). These CDs are pH-dependent, so a novel label-free florescent sensor array can be constructed by utilizing buffers with various pH levels, which leads to distinctive fluorescence response patterns upon being challenged with metal ions for their pattern recognition. The results demonstrate that large-scale detection of metal ions can be achieved with as little as 3 types of sensors. Additionally, the sensors are able to discriminate between various metal ion concentrations and mixtures of different metal ions. The technique demonstrates potential uses in water quality monitoring by promising straightforward, quick, sensitive, and potent discrimination of metal ions.

Continuous Preparation of Semiconducting Polymer Nanoparticles with Varied Sizes for Online Fluorescence Sensing via a Laser-Tailored 3D Microfluidic Chip.

Microfluidic chips are in critical demand for emerging applications in material synthesis and biosensing. Herein, we relied on ultrafast laser-processing technology to fabricate a three-dimensional (3D) microfluidic chip, in which semiconducting polymer nanoparticles (SPNs) were continuously synthesized with tunable size and SPN-involved online fluorescence sensing was implemented. A homogeneous distribution of SPNs can be readily realized due to the efficient mixing and powerful vortices of the 3D microfluidic chip, which prevents SPNs from aggregating throughout the synthesis process. Moreover, in the optimized conditions, we unveiled unique SPNs with an ultrasmall particle size (<3 nm) and good monodispersity. By integrating with the high-performance fluorescence of SPNs and 3D microfluidic chip, we further developed an online sensing platform for ratiometric fluorescence assays of H2O2 and oxidase-catalyzed substrates (e.g., glucose), in which a composite of SPNs and neutral red (NR) (SPNs/NR) was used as the mediator. The limit of detection (LOD) for H2O2 is 0.48 µM, and the LOD for glucose is 3.33 µM via the presented platform. This 3D microfluidic synthesis-and-sensing platform provides a new avenue for the facile production of nanoparticles and offers exciting prospects in the field of online sensing biomarkers.

Au/Lum/RhB@Ag-DMcT ICP-Based Double-Ratio Colorimetric and Fluorometric Dual Mode Assay and Multi-Responsive Coffee Ring Chips for Point-of-Use Analysis of Phosphate Ions.

In this work, by fully exploring the stimulus response of the guest-functionalized infinite coordination polymers (ICPs), a double-ratio colorimetric and fluorometric dual mode assay and multi-responsive coffee ring chips for point-of-use analysis of phosphate ions (Pi) were proposed. First, the complex host-guest interactions were rationally designed to obtain Au/Lum/RhB@Ag-DMcT ICPs. The composite ICPs exhibited a purple-blue color resulted from the modulated localized surface plasmon resonance (LSPR) of the Au core, and a blue fluorescence color stemmed from the unique aggregation-induced-emission (AIE) of Luminol (Lum) and the aggregation-caused-quenching (ACQ) of rhodamine B (RhB). With the presence of Pi, the host-guest interactions of the shell within Au/Lum/RhB@Ag-DMcT ICPs were interrupted to release Au core, Lum, and RhB in a dispersed state. Consequently, the color of the solution changed to purple-red (the mixed color of the Au core and RhB guest), and the fluorescence color turned to orange-red (AIE of Lum decreased, while the ACQ of RhB recovered). This constituted the sensing mechanism for dual-mode Pi assay with the double ratiometric response. Second, during the stimulus response, the surface wettability/size/amount of Au/Lum/RhB@Ag-DMcT ICPs simultaneously altered. These changes were reflected in the form of the coffee ring deposition pattern variances on the glass substrate and served as signal readouts for the exploration of multi-responsive coffee ring chips for the first time. Quantitative Pi detection with high accuracy and reliability in real samples was thereby realized, which offered an opportunity for the point-of-use analysis of Pi in resources-limited areas in a high-throughput fashion.

Wearable Clinic: From Microneedle-Based Sensors to Next-Generation Healthcare Platforms.

The rapid development of wearable biosensing calls for next-generation devices that allow continuous, real-time, and painless monitoring of health status along with responsive medical treatment. Microneedles have exhibited great potential for the direct access of dermal interstitial fluid (ISF) in a minimally invasive manner. Recent studies of microneedle-based devices have evolved from conventional off-line detection to multiplexed, wireless, and integrated sensing. In this review, the classification and fabrication techniques of microneedles are first introduced, and then the representative examples of microneedles for transdermal monitoring with different sensing modalities are summarized. State-of-the-art advances in therapeutic and closed-loop systems are presented to formulate guidelines for the development of next-generation microneedle-based healthcare platforms. The potential challenges and prospects are discussed to pave a new avenue toward pragmatic applications in the real world.

Ultrasensitive therapeutic drug monitoring of methotrexate by a structure-switching aptamer with cascade primer exchange reaction.

As a folate antagonist, methotrexate (MTX) has been widely used in clinics with good effects on various tumors and inflammatory diseases. While the optimum dosage and total body clearance of MTX usually varies between individuals and even low-dose MTX has side effects, high-dose MTX may cause life-threatening side effects. Therefore, a convenient and simple method toward MTX sensing is highly demanded. Herein, we report a highly sensitive and selective method for therapeutic drug monitoring (TMD) of MTX by integrating a highly specific MTX-dependent structure-switching aptamer with a primer exchange reaction-based signal amplification technique. The detection limit is down to 1.7 nM with a linear range from 0.01 to 1 µM in buffer. More importantly, the sensing strategy can effectively detect MTX in a complex bio-environment with a linear response range from 0.05 to 2 µM and a LOD of 12.4 nM in 10% FBS and a range of 0.2 to 5 µM with a LOD of 63.73 nM in 10% whole blood. Considering the high sensitivity and selectivity and good performance in blood, the method reported herein paves a new avenue for the effective determination of MTX in clinics.

High-Performance Extended-Gate Field-Effect Transistor for Kinase Sensing in Aß Accumulation of Alzheimer's Disease.

An amyloid-beta peptide (Aß) is generally believed to be a pathological marker of Alzheimer's disease (AD), but it is still of great significance to explore the upstream and downstream relationship of Aß in AD. It is previously reported that c-Abl, a nonreceptor tyrosine kinase, can be activated by Aß, but the interaction between Aß and c-Abl is still unknown. Herein, an extended-gate field-effect transistor (EG-FET)-based sensor has been developed to monitor the level of c-Abl with high sensitivity and selectivity. Our peptide-functionalized EG-FET sensor as the signal transducer can follow c-Abl activity with electron transfer by its specific phosphorylation. The sensor presents a good linear correlation over c-Abl concentrations of 1 pg/mL to 3.05 µg/mL. The sensor was successfully applied to quantify c-Abl activity in the brain tissue of AD transgenic mice, and the interaction between c-Abl and Aß in AD mice was explored by administering the c-Abl inhibitor (imatinib) and the agonist (DPH). Our work is expected to provide an important reference for early diagnosis and treatment of AD.

Aptamer-engineered extended-gate field-effect transistor device for point-of-care therapeutic drug monitoring.

Herein, we report a portable point-of-care testing (POCT) device based on an aptamer-engineered extended-gate field-effect transistor (EG-FET) for therapeutic monitoring of the drug methotrexate. This method was shown to be highly sensitive, efficient, and convenient to use, features contributing to its realizing a clinical detection of drugs in blood.

Progress on the reaction-based methods for detection of endogenous hydrogen sulfide.

Hydrogen sulfide (H2S) is a biologically signaling molecule that mediates a wide range of physiological functions, which is frequently misregulated in numerous pathological processes. As such, measurement of H2S holds great attention due to its unique physiological and pathophysiological roles. Currently, a variety of methods based on the H2S-involved reactions have been reported for detection of endogenous H2S, bearing the advantages of good specificity and high sensitivity. This review describes in detail the types of reactions, their mechanisms, and their applications in biological research, thus hopefully providing some guidelines to the researchers in this field for further investigation.

Coordination of Ligand-Protected Metal Nanoclusters and Glass Nanopipettes: Conversion of a Liquid-Phase Fluorometric Assay into an Enhanced Nanopore Analysis.

We propose a unique concept for transforming the liquid-phase fluorometric assay into an enhanced nanopore analysis, which is based on the analyte binding-mediated changes in the surface chemistry of noble metal nanostructures in a confined space. In a proof-of-concept trial, the bovine serum albumin-protected gold nanoclusters (BSA-Au NCs) were designed as the sensing unit for biothiol determination. Through the specific interaction between biothiols and BSA-Au NCs, the validation system not only performed well in aqueous fluorescent detection but also can be developed into a more selective and sensitive nanopore sensor. In the confined space of the nanopore, the BSA-Au NC film with high density formed, and the addition of biothiols triggered the fluorescence enhancement as well as the ionic current response, hence leading to the construction of the dual-signal-output (fluorescence/ion current signal) system. The fluorescence signal proved that the ionic current change corresponded to the specific recognition process, improving the reliability of our nanopore method. Moreover, the ionic current response from the BSA-Au NC film can be used to quantify cysteine in a broad dynamic range of 0.001-1 pM with a detection limit as low as 1 fM. Such a strategy can be used to detect biothiols in complex biological fluids such as human serum. Therefore, the present work provided a new design strategy for a glass nanopipette sensor inspired by the principles of numerous and diverse fluorometric assays. It also sheds light on how the coupling of electrical and optical signals improves the accuracy, sensitivity, and selectivity of the glass nanopipette platform.

Tailoring Oxygen-Containing Groups on Graphene for Ratiometric Electrochemical Measurements of Ascorbic Acid in Living Subacute Parkinson's Disease Mouse Brains.

Ascorbic acid (AA), a major antioxidant in the central nervous system (CNS), is involved in withstanding oxidative stress that plays a significant role in the pathogenesis of Parkinson's disease (PD). Exploring the AA disturbance in the process of PD is of great value in understanding the molecular mechanism of PD. Herein, by virtue of a carbon fiber electrode (CFE) as a matric electrode, a three-step electrochemical process for tailoring oxygen-containing groups on graphene was well designed: potentiostatic deposition was carried out to fabricate graphene oxide on CFE, electrochemical reduction that assisted in removing the epoxy groups accelerated the electron transfer kinetics of AA oxidation, and electrochemical oxidation that increased the content of the carbonyl group (C═O) generated an inner-reference signal. The mechanism was solidified by ab initio calculations by comparing AA absorption on defected models of graphene functionalized with different oxygen groups including carboxyl, hydroxyl, epoxy, and carbonyl. It was found that epoxy groups would hinder the physical absorption of AA onto graphene, while other functional groups would be beneficial to it. Biocompatible polyethylenedioxythiophene (PEDOT) was further rationally assembled to improve the antifouling property of graphene. As a result, a new platform for ratiometric electrochemical measurements of AA with high sensitivity, excellent selectivity, and reproducibility was established. In vivo determination of AA levels in different regions of living mouse brains by the proposed method demonstrated that AA decreased remarkably in the hippocampus and cortex of a subacute PD mouse than those of a normal mouse.

Colorimetric recognition of lanthanide ions with a complexometric indicator array.

A colorimetric sensor array based on complexometric indicators is proposed for pattern recognition of lanthanide ions. The complexometric indicators have abundant functional groups and can act as a platform for chromogenic reaction with various metal ions, including lanthanide ions. The subtle difference of the lanthanide ions' structure results in the difference of absorbance response between lanthanide ions and two chromogenic indicators (Alizarin Red and Erichrome Black T) in Tris-HCl buffer with two different pHs (i.e., pH 7.4 and pH 8.5, colorimetric sensor array). Fourteen lanthanide ions were distinguished well with the newly designed colorimetric sensor array. The sensor array has the potential to distinguish between different concentrations of lanthanide ions and their mixtures. Moreover, the results in actual samples indicate the future practical applications of this sensor array in environmental analysis.

An enhanced fluorescent probe through the strategy of using MgWO4 nanosheets to enhance terbium ion luminescence for highly sensitive and point-of-care visual quantitative testing of ciprofloxacin integrated with a low-cost smartphone-based platform.

In this work, MgWO4 nanosheets have been successfully synthesized by a simple hydrothermal method, and the morphology and composition of the MgWO4 nanosheets are characterized by SEM, TEM, XPS, and UV-vis. The results show that the as-prepared MgWO4 nanosheets have a triclinic symmetry phase and an obvious two-dimensional layered structure. Studies have shown that the MgWO4 semiconductor nanosheets can adjust the energy level, which significantly enhances the visible light absorption and the separation and transfer of photogenerated electrons, which facilitates the generation of photogenerated electrons. We use this feature to boost a terbium ion (Tb3+)-ciprofloxacin (CIP) system to enhance the luminescence, so as to achieve highly sensitive detection of CIP. The mechanism of Tb3+-MgWO4 for CIP detection is the effective energy transfer from WO42- in MgWO4 nanosheets to Tb3+-CIP, thereby enhancing the characteristic emission of Tb3+ and enhancing the sensitivity of CIP detection. The linear response of the Tb3+-MgWO4 enhanced fluorescent probe is in the range from 10 nM to 20 µM, and the detection limit (LOD) is 2 nM. In addition, we tested the recovery in spiked river water and mouse serum. Experiments have shown that the recovery of spiked samples is 97-102.2%, while the relative standard deviation (RSD) is less than 5.53%. The possible interfering substances in environmental samples will not interfere with the detection of CIP with the Tb3+-MgWO4 enhanced fluorescent probe. At the same time, the development of a smartphone-based portable device provides the possibility of CIP on-site detection. Our work provides a simple, fast, highly sensitive and stable method for detecting CIP in living organisms and the environment. Importantly, the strategy of MgWO4 nanosheet boosted terbium ion luminescence expands the application range of semiconductor nanomaterials.

A ratiometric electrochemical microsensor for monitoring chloride ions in vivo.

Chloride ion (Cl-), the most common anion in animal brain, has been verified to play a vital role in maintaining normal physiological processes. Thus, development of a reliable platform to determine Cl- is of great significance for brain research involving Cl-. In this work, a ratiometric electrochemical microsensor (REM) for the in vivo measurement of cerebral Cl- was designed. To prepare REM, uniform Ag nanoparticles (Ag NPs) with nano-level sizes were synthesized via an adsorption-reduction process, which served as selective recognition elements for Cl- determination, while methylene blue (MB) was absorbed and acted as an inner reference unit to avoid the environmental interference of complicated brain systems. As a result, this developed REM exhibited high sensitivity and selectivity, as well as good stability, reproducibility and anti-biofouling. This reliable approach was established to monitor Cl- in mouse brain.

Stimulus Response of TPE-TS@Eu/GMP ICPs: Toward Colorimetric Sensing of an Anthrax Biomarker with Double Ratiometric Fluorescence and Its Coffee Ring Test Kit for Point-of-Use Application.

In this work, by fully exploring the stimulus response of infinite coordination polymer nanoparticles (ICPs) and by taking advantage of the particular optical properties of ICP guest tetra(4-sulfophenyl)ethene (TPE-TS) with adjustable monomer emission (ME) and aggregation-induced emission (AIE), we demonstrated a novel sensing mechanism for an anthrax biomarker dipicolinic acid (DPA) based on the competitive coordination interaction regulating the structure of TPE-TS@Eu/GMP ICPs. The double ratiometric fluorescence stemmed from triple response of TPE-TS@Eu/GMP ICPs without spectral cross-interference (ME and AIE from TPE-TS and sensitized emission from Eu/DPA) and a corresponding blue-to-red fluorescent color change, which not only benefited the direct detection of DPA with high sensitivity and selectivity, but also offered a great opportunity to realize real-time monitoring of DPA released by Bacillus subtilis spores. Furthermore, the coffee ring deposition patterns on a test paper were innovatively tuned by the quantity and morphology changes of TPE-TS@Eu/GMP ICPs during their stimulus response toward DPA, which could be exploited as expanded signal channels. By integrating a multichannel responsive coffee ring test kit with image recognition and processing application installed on smartphones, point-of-use analysis of DPA could be realized in a low-cost and high-throughput fashion.

Sensitive and Selective Measurement of Hydroxyl Radicals at Subcellular Level with Tungsten Nanoelectrodes.

Hydroxyl radical (•OH) is an essential reactive oxygen species involved in critical cell functions. However, the mechanisms controlling its subcellular localization and intracellular level during health and disease remain poorly understood. This is due to the challenge of detecting •OH that are highly reactive and consequently short-lived (in vivo half-life of ∼10-9 s). Herein, we present tungsten nanoelectrodes functionalized with stable 1-hexanethiol (HAT) for selective and sensitive detection of •OH at the subcellular level via the destruction of the self-assembled monolayer of HAT on the nanoelectrode tip. Taking advantage of the ultrasmall nanotip and the super mechanical toughness, the tungsten nanoelectrode could easily penetrate a single living cell without inducing any observable damage. Controlled by a high precision micromanipulator, the •OH level in RAW 264.7 murine macrophages under amyloid ß (Aß) induced oxidative stress were first investigated by the nanoelectrodes at the subcellular level. Moreover, the results revealed the cordycepin-mediated cytoprotection of macrophages through modulation of PI3K/Akt pathway activity and introduction of heme oxygenase-1 (HO-1). We believe that the developed nanoelectrochemical method has shown great capacities for the study of potential drugs for therapeutic intervention of Alzheimer's disease.

Facile Ratiometric Electrochemical Sensor for In Vivo/Online Repetitive Measurements of Cerebral Ascorbic Acid in Brain Microdiaysate.

The in vivo monitoring of ascorbic acid (AA) following physiological and pathological events is of great importance because AA plays a critical role in brain functions. The conventional electrochemical sensors (ECSs) usually suffered from poor selectivity and sluggish electron transfer kinetics for cerebral AA oxidation. The exploitation of ECSs adapt to the electrochemical detection (ECD)-microdialysis system, here we reported a facile ratiometric electrochemical sensor (RECS) for in vivo/online repetitive measurements of cerebral AA in brain microdiaysate. The sensor were constructed by careful electrodeposition of graphene oxide (GO) onto glassy carbon (GC) electrodes. Methylene blue (MB) was electrostatically adsorbed onto the GO surface as a built-in reference to achieve ratiometric detection of AA. The subsequent proper electroreduction treatment was able to readily facilitate the oxidation of AA at a relatively negative potential (-100 mV) and the oxidation of MB at separated potential (-428 mV). The in vitro experiments demonstrated that the RECS exhibited high sensitivity (detection limit: 10 nM), selectivity, and stability toward AA determination, enabling the in vivo/online repetitive measurement of cerebral AA in brain microdiaysate with high reliability. As a result, the designed RECS was successfully applied in the ECD-microdialysis system to in vivo/online repetitive monitoring the dynamic change of cerebral AA in the progress of the global cerebral ischemia/reperfusion events. More, the microinjection of endogenous AA and AA oxidase (AAOx) verified the reliability of the proposed RECS for in vivo/online repetitive cerebral AA detection. This proposed sensor filled the gap that no rational electrochemical sensor has been developed for the ECD-microdialysis system since its creation by the Mao group in 2005, which provided a reliable and effective method for brain chemistry research.

Molybdenum disulfide nanosheets-based fluorescent "off-to-on" probe for targeted monitoring and inhibition of ß-amyloid oligomers.

A novel and simple "off-to-on" fluorescent sensing platform for ß-amyloid oligomers (Aßo) was developed based on dye (FAM)-labeled single-strand DNA (FAM-ssDNA)-conjugated molybdenum disulfide nanosheets (MoS2 NSs). Due to strong adsorption of ss-DNA to the surface of MoS2 NSs, the fluorescence of FAM was quenched remarkably, leading to a fluorescent "off" state. However, in the presence of Aßo, a hybrid structure between Aßo and FAM-ssDNA resulted in the dissociation of FAM-ssDNA from MoS2 NSs and an obvious fluorescence recovery transformed the fluorescence to an "on" state. The developed fluorescence sensing assay showed a good linear relationship toward Aßo ranging from 0.01 to 20 µM (R2 = 0.994) with a satisfactory detection limit of 3.1 nM. Practical samples of hippocampus and cortex tissues from APP/PS1 double transgenic AD mice were applied to demonstrate feasibility of the assay. Moreover, we found that similar to MoS2 nanoparticles, MoS2 NSs possessed therapeutic effects on Alzheimer's disease (AD) by inhibiting Aß aggregations and degrading the previously formed Aß fibrils. Collectively, the high sensitivity, specificity, and good biocompatibility along with an efficient anti-aggregation ability, the presented fluorescent strategy with MoS2 NSs demonstrated their promising potential for future AD-related research.

Interface engineering of microelectrodes toward ultrasensitive monitoring of ß-amyloid peptides in cerebrospinal fluid in Alzheimer's disease.

Ultrasensitive detection of monomeric ß-amyloid peptides is of fundamental significance for studying the pathological progression of Alzheimer's disease (AD). In this article, by facilely engineering a gold microelectrode interface, we developed a novel electrochemical biosensor for sensitive and selective monitoring of ß-amyloid peptide (Aß) monomers in cerebrospinal fluid (CSF). Through specific Cu2+-Aß-hemin coordination, Aß directed the assembly of Cu2+-PEI/AuNPs-hemin nanoprobes into network aggregates on a microelectrode interface, which promoted the enrichment of Aß monomers on the microelectrode. Furthermore, the AuNP aggregate promotes the deposition of silver nanoparticles, which were utilized for the electrochemical stripping analysis of the Aß monomer. The proposed method displayed ultra-sensitivity for Aß monomers with the detection limit down to 0.2 pM. Besides, high selectivity toward Aß monomers was observed. These remarkable analytical performances render the electrochemical biosensor useful for evaluating the dynamic change of Aß monomer level in CSF of live mice with AD, promoting the investigation of the role that Aß monomers play in brain events.

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

In this work, we prepared a type of multiplexing upconversion nanoparticle (UCNP). There are three fluorescence emission peaks when our UCNPs are excited with 980 and 808 nm lasers. These fluorescence peaks of UCNPs can be quenched ("turn off") to varying degrees via fluorescence resonance energy transfer (FRET) when the UCNPs are coated with a polydopamine (PDA) layer, which is a universal quencher self-polymerized from dopamine (DA). Here, we create a novel single-component nanoprobe that can be used for the pattern recognition of antioxidants in a "turn on" manner by integrating with the prevention of PDA formation with an antioxidant. Our sensing strategy is based on the recovery of the fluorescence intensity of three emission peaks to different degrees due to different antioxidants with differential inhibition of PDA formation. Then, these three fluorescence emission peaks of UCNPs are innovatively selected as the sensor array, which enables us to discriminate multiple antioxidants and their mixtures. Simultaneously, the sensor array shows excellent performance in the chiral discrimination of cysteine enantiomers. This is a novel, innovative sensor array that requires only a single component to achieve the upconversion fluorescence pattern and recognize chiral molecules, and it elucidates a more innovative concept towards widespread applications.