A Single Biosensor for Evaluating the Levels of Copper Ion and L ‐Cysteine in a Live Rat Brain with Alzheimer's Disease

Progress in appended calix[4]arene-based receptors for selective recognition of copper ions

In the past two decades, there has been significant progress in the design and development of synthetic receptors for molecular recognition as they find application in the field of chemical, biological, medical, and environmental sciences. Synthetic receptors based on calix systems appended with fluorogenic and chromogenic groups have gained considerable attention for sensing and recognition of ions and molecules. Copper (Cu2+) is an essential element required in trace amounts in all living organisms to carry out various biological processes. The aim of this review is to summarize advancement in π-conjugated fluorogenic and chromogenic groups appended to calix[4]arene motifs for detection and quantitation of Cu2+ ion. The focus is to present a comprehensive account of extended calix[4]arene systems with different linkers and highlight the unique design and binding characteristics for the recognition and sensing of Cu2+ ions.

Implantable Electrochemical Sensors for Brain Research

Implantable electrochemical sensors provide reliable tools for in vivo brain research. Recent advances in electrode surface design and high-precision fabrication of devices led to significant developments in selectivity, reversibility, quantitative detection, stability, and compatibility of other methods, which enabled electrochemical sensors to provide molecular-scale research tools for dissecting the mechanisms of the brain. In this Perspective, we summarize the contribution of these advances to brain research and provide an outlook on the development of the next generation of electrochemical sensors for the brain.

Real-time Tracking and Sensing of Cu+ and Cu2+ with a Single SERS Probe in the Live Brain: Toward Understanding Why Copper Ions Were Increased upon Ischemia

The imbalance of Cu⁺ and Cu²⁺ in the brain is closely related to neurodegenerative diseases. However, it still lacks of effective analytical methods for simultaneously determining the concentrations of Cu⁺ and Cu²⁺ . Herein, we created a novel SERS probe (CuSP) to real-time track and accurately quantify extracellular concentrations of Cu⁺ and Cu²⁺ in the live brain. The present CuSP probe demonstrated specific ability for recognition of Cu⁺ and Cu²⁺ in a dual-recognition mode. Then, a microarray consisting of 8 CuSP probes with high tempo-spatial resolution and good accuracy was constructed for tracking and simultaneously biosensing of Cu⁺ and Cu²⁺ in the cerebral cortex of living brain. Using our powerful tool, it was found that that the concentrations of Cu²⁺ and Cu⁺ were increased by ≈4.26 and ≈1.80 times upon ischemia, respectively. Three routes were first discovered for understanding the mechanisms of the increased concentrations of Cu⁺ and Cu²⁺ during ischemia.

Long-Term Tracking and Dynamically Quantifying of Reversible Changes of Extracellular Ca2+ in Multiple Brain Regions of Freely Moving Animals

Understanding physiological and pathological processes in the brain requires tracking the reversible changes in chemical signals with long-term stability. We developed a new anti-biofouling microfiber array to real-time quantify extracellular Ca²⁺ concentrations together with neuron activity across many regions in the mammalian brain for 60 days, in which the signal degradation was < ca. 8 %. The microarray with high tempo-spatial resolution (ca. 10 μm, ca. 1.3 s) was implanted into 7 brain regions of free-moving mice to monitor reversible changes of extracellular Ca²⁺ upon ischemia-reperfusion processes. The changing sequence and rate of Ca²⁺ in 7 brain regions were different during the stroke. ROS scavenger could protect Ca²⁺ influx and neuronal activity after stroke, suggesting the significant influence of ROS on Ca²⁺ overload and neuron death. We demonstrated this microarray is a versatile tool for investigating brain dynamic during pathological processes and drug treatment.

A Robust Au-C≡C Functionalized Surface: Toward Real-Time Mapping and Accurate Quantification of Fe2+ in the Brains of Live AD Mouse Models

Described here is that Au-C≡C bonds showed the highest stability under biological conditions, with abundant thiols, and the best electrochemical performance compared to Au-S and Au-Se bonds. The new finding was also confirmed by theorical calculations. Based on this finding, a specific molecule for recognition of Fe²⁺ was designed and synthesized, and used to create a selective and accurate electrochemical sensor for the quantification of Fe²⁺ . The present ratiometric strategy demonstrates high spatial resolution for real-time tracking of Fe²⁺ in a dynamic range of 0.2-120 μM. Finally, a microelectrode array with good biocompatibility was applied in imaging and biosensing of Fe²⁺ in the different regions of live mouse brains. Using this tool, it was discovered that the uptake of extracellular Fe²⁺ into the cortex and striatum was largely mediated by cyclic adenosine monophosphate (cAMP) through the CREB-related pathway in the brain of a mouse with Alzheimer's disease.

Rational Design of Specific Recognition Molecules for Simultaneously Monitoring of Endogenous Polysulfide and Hydrogen Sulfide in the Mouse Brain

A biosensor was created for the simultaneous monitoring of endogenous H₂ S_n and H₂ S in mouse brains and exploring their roles in activation of the TRPA1 channel under two types of brain disease models: ischemia and Alzheimer's disease (AD). Based on DFT calculations and electrochemical measurements, two probes, 3,4-bis((2-fluoro-5-nitrobenzoyl)oxy)-benzoic acid (M_PS-1 ) and N-(4-(2,5-dinitrophenoxy) phenyl)-5-(1, 2-dithiolan-3-yl)pentanamide (M_HS-1 ), were synthesized for specific recognition of H₂ S_n and H₂ S. Through co-assembly of the two probes at the mesoporous gold film with good anti-biofouling ability and electrocatalytic activity, this microsensor showed high selectivity for H₂ S_n and H₂ S against potential biological interferences. The biosensor can simultaneously determine the concentration of H₂ S_n from 0.2 to 50 μm, as well as that of H₂ S from 0.2 to 40 μm. The expression of TRPA1 protein positively correlated with levels of H₂ S_n under both ischemia and AD.

A colorimetric assay for ultrasensitive detection of copper (II) ions based on pH-dependent formation of heavily doped molybdenum oxide nanosheets

Here we report a simple and low-cost colorimetric assay for ultrasensitive detection of copper (II) ions (Cu²⁺) based on pH-dependent formation of plasmonic MoO_3-x nanosheets. The reaction between ascorbic acid (AA) and Cu²⁺ gives birth to hydrogen ions, which remarkably promotes the reduction of MoO₃ nanosheets by AA to form oxygen vacancies-rich MoO_3-x nanosheets that increase the free carrier concentration, generating a strong local surface plasmon resonance (LSPR) absorption. The Cu²⁺-triggered LSPR is utilized for development of the colorimetric assay. Under the optimal experimental conditions, this colorimetric assay can be used for selective detection of Cu²⁺, and the limit of detection is 0.8 nM, which is lower than that of most of the reported methods. Additionally, the present colorimetric assay has also been successfully employed for Cu²⁺ determination in real serum and human hair samples with satisfactory recoveries ranging from 96% to 108%.

A SERS Optophysiological Probe for the Real-Time Mapping and Simultaneous Determination of the Carbonate Concentration and pH Value in a Live Mouse Brain

To have a profound understanding of the physiological and pathological processes in a brain, both chemical and electrical signals need to be recorded, but this is still very challenging. Herein, micrometer- to nanometer-sized SERS optophysiological probes were created to determine both the CO₃ ^2- concentration and the pH in live brains and neurons because both species play important roles in regulating the acid-base balance in the brain. A ratiometric SERS microarray of eight microprobes with tip sizes of 5 μm was established and used for the first time for real-time mapping and simultaneous quantification of CO₃ ^2- and pH in a live brain. We found that both the CO₃ ^2- concentration and the pH value dramatically decreased under ischemic conditions. The present SERS technique can be combined with electrophysiology without cross-talk to record both electrical and chemical signals in brains. To deepen our understanding of the mechanism of ischemia on the single-cell level, a SERS nanoprobe with a tip size of 200 nm was developed for use in a single neuron.

Real-time monitoring of peroxynitrite (ONOO−) in the rat brain by developing a ratiometric electrochemical biosensor

As a reactive oxygen species (ROS), peroxynitrite (ONOO⁻) generated by nitric oxide (NO) and superoxide anion (O₂˙⁻) plays important roles in physiological and pathological processes in the brain.

Saccharomyces-derived carbon dots for biosensing pH and vitamin B 12

Photoluminescence(PL) nano-biosensors that can be used for accurately and reliably monitoring pH and vitamin hold a great promise in biology and medicine. Herein, a high quantum yield of 16% saccharomyces-derived N-doped carbon dots (s-N-CDs) was synthesized through a simple and one-pot microwave-assisted hydrothermal approach. The produced s-N-CDs are an excellent multi-functional biosensor for the applications of pH sensing and vitamin probing. Fluorescence intensity and fluorescence lifetime dramatically increases with pH decreasing from 14 to 2. Moreover, the fluorescence intensity presents highly reversible abilty from 13 to 2 without any profound attenuation after ten consecutive circles. More importantly, the CDs prepared herein are sound option for assaying cobalamin (VB 12) based fluorescence resonance energy transfer (FRET) with a superior low detection limit of 2.19 μM.

Metal-Organic Framework-Based Selective Sensing of Biothiols via Chemidosimetric Approach in Water

Selective detection of biothiols holds prime importance owing to the role of varied concentrations of biothiols in various diseases, thus demanding extensive research for developing materials toward selective sensing. In this study, we targeted postsynthetic modification (PSM) approach for imparting desired functionality to chemically stable UiO-66-NH₂ metal-organic framework, which exhibits highly selective sensing toward biothiols. The appended dinitrobenzenesulfonyl group reacts with biothiols via chemidosimetric approach. As a consequence, the probe exhibits a turn on response, which holds immense importance for facile biological studies.

N-Doped Graphene Quantum Dots-Decorated V2O5 Nanosheet for Fluorescence Turn Off-On Detection of Cysteine

The development of a fast-response sensing technique for detection of cysteine can provide an analytical platform for prescreening of disease. Herein, we have developed a fluorescence turn off-on fluorescence sensing platform by combining nitrogen-doped graphene quantum dots (N-GQDs) with V₂O₅ nanosheets for the sensitive and selective detection of cysteine in human serum samples. V₂O₅ nanosheets with 2-4 layers are successfully synthesized via a simple and scalable liquid exfoliation method and then deposited with 2-8 nm of N-GQDs as the fluorescence turn off-on nanoprobe for effective detection of cysteine in human serum samples. The V₂O₅ nanosheets serve as both fluorescence quencher and cysteine recognizer in the sensing platform. The fluorescence intensity of N-GQDs with quantum yield of 0.34 can be quenched after attachment onto V₂O₅ nanosheets. The addition of cysteine triggers the reduction of V₂O₅ to V⁴⁺ as well as the release of N-GQDs within 4 min, resulting in the recovery of fluorescence intensity for the turn off-on detection of cysteine. The sensing platform exhibits a two-stage linear response to cysteine in the concentration range of 0.1-15 and 15-125 μM at pH 6.5, and the limit of detection is 50 nM. The fluorescence response of N-GQD@V₂O₅ exhibits high selectivity toward cysteine over other 22 electrolytes and biomolecules. Moreover, this promising platform is successfully applied in detection of cysteine in human serum samples with excellent recovery of (95 ± 3.8) - (108 ± 2.4)%. These results clearly demonstrate a newly developed redox reaction-based nanosensing platform using N-GQD@V₂O₅ nanocomposites as the sensing probe for cysteine-associated disease monitoring and diagnosis in biomedical applications, which can open an avenue for the development of high performance and robust sensing probes to detect organic metabolites.

Label-Free Electrochemical Biosensor for Monitoring of Chloride Ion in an Animal Model of Alzhemier's Disease

The potential damage of Alzheimer's disease (AD) in brain function has attracted extensive attention. As the most common anion, Cl^- has been indicated to play significant roles in brain diseases, particularly in the pathological process of AD. In this work, a label-free selective and accurate electrochemical biosensor was first developed for real-time monitoring of Cl^- levels in a mouse brain model of AD and rat brain upon global cerebral ischemia. Silver nanoparticles (AgNPs) were designed and synthesized as selective recognition element for Cl^-, while 5'-MB-GGCGCGATTTT-SH-3' (SH-DNA-MB, MB = methylene blue) was selected as an inner reference molecule for a built-in correction to avoid the effects from the complicated brain. The electrochemical biosensor showed high accuracy and remarkable selectivity for determination of Cl^- over other anions, metal ions, amino acids, and other biomolecules. Furthermore, three-dimensional nanostructures composed of single-walled carbon nanotubes (SWNTs) and Au nanoleaves were assembled on the carbon fiber microelectrode (CFME) surface to enhance the response signal. Finally, the developed biosensor with high analytical performance, as well as the unique characteristic of CFME itself including inertness in live brain and good biocompatibility, was successfully applied to in vivo determination of Cl^- levels in three brain regions: striatum, hippocampus, and cortex of live mouse and rat brains. The comparison of average levels of Cl^- in normal striatum, hippocampus, and cortex of normal mouse brains and those in the mouse model brains of AD was reported. In addition, the results in rat brains followed by cerebral ischemia demonstrated that the concentrations of Cl^- decreased by 19.8 ± 0.5% (n = 5) in the striatum and 27.2 ± 0.3% (n = 5) in hippocampus after cerebral ischemia for 30 min, but that negligible change in Cl^- concentration was observed in cortex.

Ratiometric SERS imaging and selective biosensing of nitric oxide in live cells based on trisoctahedral gold nanostructures

Herein, a ratiometric SERS probe was created for monitoring nitric oxide (NO) by designing a novel molecule, 3,4-diaminobenzene-thiol, and immobilizing this molecule onto trisoctahedral gold nanostructures with superior SERS capability. The established probe possessed good selectivity and biocompatibility, high sensitivity and accuracy, thus enabling imaging and biosensing of NO in live cells.

A simple functional carbon nanotube fiber for in vivo monitoring of NO in a rat brain following cerebral ischemia

A simple ratiometric electrochemical biosensor for NO monitoring in rat brain following cerebral ischemia was developed based on a carbon nanotube fiber modified with hemin.

Electrochemical sandwich-type biosensors for α-1 antitrypsin with carbon nanotubes and alkaline phosphatase labeled antibody-silver nanoparticles

A novel sandwich-type biosensor was developed for the electrochemical detection of α-1 antitrypsin (AAT, a recognized biomarker for Alzheimer's disease). The biosensor was composed of 3, 4, 9, 10-perylene tetracarboxylic acid/carbon nanotubes (PTCA-CNTs) as a sensing platform and alkaline phosphatase-labeled AAT antibody functionalized silver nanoparticles (ALP-AAT Ab-Ag NPs) as a signal enhancer. CNTs offer high surface area and good electrical conductivity. Importantly, Ag NPs could increase the amount of ALP on the sensing surface and the ALP could dephosphorylate 4-amino phenyl phosphate (APP) enzymatically to produce electroactive species 4-aminophenol (AP). For detecting AAT based on the sandwich-type biosensor, the results show that the peak current value of AP using ALP-AAT Ab-Ag NPs as signal enhancer is much higher than that by using ALP-AAT Ab bioconjugate (without Ag NPs), the biosensor exhibited desirable performance for AAT determination with a wide linearity in the range from 0.05 to 20.0pM and a low detection limit of 0.01pM. Finally, the developed sensor was successfully applied to the analysis of AAT concentration in serum samples.

In vivo monitoring of local pH values in a live rat brain based on the design of a specific electroactive molecule for H+

We have developed a two-channel electrochemical ratiometric biosensor for local pH determination in different regions of the rat brain with remarkable selectivity and accuracy, and report the accurate pH values.