Au-S Bond Research Articles

Electrochemical Immunosensor Using Electroactive Carbon Nanohorns for Signal Amplification for the Rapid Detection of Carcinoembryonic Antigen

In this work, a novel sandwich-type electrochemical immunosensor was developed for the quantitative detection of the carcinoembryonic antigen, an important tumor marker in clinical tests. The capture antibodies were immobilized on the surface of a gold disk electrode, while detection antibodies were attached to redox-tagged single-walled carbon nanohorns/thionine/AuNPs. Both types of antibody immobilization were carried out through Au-S bonds using the novel photochemical immobilization technique that ensures control over the orientation of the antibodies. The electroactive SWCNH/Thi/AuNPs nanocomposite worked as a signal tag to carry out both the detection of carcinoembryonic antigen and the amplification of the detection signal. The current response was monitored by differential pulse voltammetry. A clear dependence of the thionine redox peak was observed as a function of the carcinoembryonic antigen concentration. A linear detection range from 0.001-200 ng/mL and a low detection limit of 0.1385 pg/mL were obtained for this immunoassay. The results showed that carbon nanohorns represent a promising matrix for signal amplification in sandwich-type electrochemical immune assays working as a conductive and binding matrix with easy and versatile modification routes to antibody and redox tag immobilization, which possesses great potential for clinical diagnostics of CEA and other biomarkers.

A novel sandwich impedimetric immunosensor for detection of apolipoprotein-A1 based on the gold nanoparticle-hybridized mercapto-β-cyclodextrin-Pb(II) metal-organic framework.

A novel sandwich electrochemical impedimetric immunosensor was proposed to detect apolipoprotein-A1 (Apo-A1), a common biomarker for bladder cancer. The molybdenum disulfide/graphene quantum dot (MoS2/GQD) nanocomposites were modified on the surface of a glassy carbon electrode (GCE) and used to immobilize the biotinylated antibody (Ab1) with the help of chitosan and glutaraldehyde (denoted as BSA/Ab1/CHIT/MoS2/GQD/GCE). Pb(II)-thiol-β-cyclodextrin metal-organic framework (denoted as Pb-MOF) was synthesized with lead metal ions and thiol-β-cyclodextrin ligands by a one-pot solvothermal method, and then, gold nanoparticles were modified on the surface of Pb-MOF (Pb-MOF-AuNPs) by Au-S bond, which was used as signal label for the recombinant antibody (Ab2). When the immunosensor of BSA/Ab1/CHIT/MoS2/GQD/GCE reacted with Apo-A1, Pb-MOF-AuNPs-Ab2/BSA was connected to the electrode when immunoreaction occurred, and an immune sandwich structure was formed, which led to significantly increased charge transfer resistance of electrochemical probe for ferrocyanide (II)/(III) within the frequency range 10-1 ~ 105Hz at 5 mV amplitude and the potential of 0.180V (vs. SCE). Based on this principle, the quantitative detection of Apo-A1 was established. The relative change of electrochemical resistance and the logarithmic value of Apo-A1 concentration showed a linear relationship with a linear coefficient of 0.9989 in the range 1.00pgmL-1 and 1.00μgmL-1 with the limit of detection of 0.30pgmL-1. The selectivity, repeatability, and other performance of the proposed immunosensor were also investigated. The immunosensor was successfully applied to the detection of real serum and urine samples with recovery in the range 96.4 ~ 109.1% (RSD < 3.8%), indicating that it could be helpful for the clinical diagnosis of bladder cancer.

Spherical Nucleic Acid Probe Based on 2′-Fluorinated DNA Functionalization for High-Fidelity Intracellular Sensing

Traditional spherical nucleic acids (SNAs) based on gold nanoparticles (AuNPs) assembled through Au-S covalent bonds are widely used in DNA-programmable assembly, biosensing, imaging, and therapeutics. However, biological thiols and other chemical substances can break the Au-S bonds and cause response distortion during the application process, specifically in cell environments. Herein, we report a new type of SNAs based on 2'-fluorinated DNA-functionalized AuNPs with excellent colloidal stability under high salt conditions (up to 1 M NaCl) and over a broad pH range (1-14), as well as resistance to biothiols. The fluorinated spherical nucleic acid probe (Au/FDNA probe) could detect targeted cancer cells with high fidelity. Compared to the traditional thiolated DNA-functionalized AuNP probe (Au-SDNA probe), the Au/FDNA probe exhibited a higher sensitivity to the target and a lower signal-to-background ratio. Furthermore, the Au/FDNA probe could discriminate target cancer cells in a mixed culture system. Using the proposed FDNA functionalization method, previously developed SNAs based on AuNPs could be directly adapted, which might open a new avenue for the design and application of SNAs.

Mesoporous polydopamine-based nanoplatform for enhanced tumor chemodynamic therapy through the reducibility weakening strategy

Polydopamine (PDA)-based Fenton agents attract increasing attention in tumor photothermal-enhanced chemodynamic therapy (CDT) due to their good biocompatibility and excellent loading capacity. However, PDA tends to eliminate the Fenton reaction-generated hydroxyl radical (∙OH) by its strong reducibility, which is an intractable hinder to the efficacy of CDT that need to be solved. Herein, a kind of mesoporous PDA-gold-manganese dioxide (MPDA-Au-MnO2, MPAM) nanoplatform was constructed for photothermal-enhanced CDT against tumor through the reducibility weakening strategy. The reducibility of original MPDA is effectively weakened by the oxidation role of HAuCl4 and KMnO4 during the preparation process, reducing the ∙OH scavenging ability of MPDA and benefiting the production of ∙OH. The MnO2 shell could react with GSH to release Mn2+, acting as the Fenton-like agent to generate ∙OH. The exposed Au NPs can further deplete GSH through the Au-S bond interaction. MPDA acts as the photothermal agent to generate hyperthermia under laser irradiation. MPAM shows excellent intracellular GSH scavenging ability and enhanced ∙OH production ability. After intravenous injection, MPAM can significantly suppress the growth of tumors under laser irradiation, meanwhile showing good biosafety. The developed MPDA-based nanoplatform can not only display good potential in further tumor treatments but also provide meaningful enlightenment for developing high-performance PDA or MPDA-based nanoplatforms in CDT-related applications.

Interaction of Colloidal Gold Nanoparticles with Urine and Saliva Biofluids: An Exploratory Study.

The use of gold nanoparticles for drug delivery, photothermal or photodynamic therapy, and biosensing enhances the demand for knowledge about the protein corona formed on the surface of nanoparticles. In this study, gold nanospheres (AuNSs), gold nanorods (AuNRs), and gold nanoflowers (AuNFs) were incubated with saliva or urine. After the interaction, the surface of gold nanoparticles was investigated using UV-VIS spectroscopy, zeta potential, and dynamic light scattering. The shifting of the localized surface plasmon resonance (LSPR) band, the increase in hydrodynamic diameter, and the changes in the surface charge of nanoparticles indicated the presence of biomolecules on the surface of AuNSs, AuNRs, and AuNFs. The incubation of AuNFs with saliva led to nanoparticle aggregation and minimal protein adsorption. AuNSs and AuNRs incubated in saliva were analyzed through liquid chromatography with tandem mass spectrometry (LC-MS/MS) to identify the 96 proteins adsorbed on the surface of the gold nanoparticles. Among the 20 most abundant proteins identified, 14 proteins were common in both AuNSs and AuNRs. We hypothesize that the adsorption of these proteins was due to their high sulfur content, allowing for their interaction with gold nanoparticles via the Au-S bond. The presence of distinct proteins on the surface of AuNSs or AuNRs was also investigated and possibly related to the competition between proteins present on the external layers of corona and gold nanoparticle morphology.

Five-Coordinated Dysprosium Single-Molecule Magnet Functionalized by the SMe Group.

A five-coordinate mononuclear Dy(III) complex with a C4v geometry (square-pyramid), [Dy(X)(DBP)2(TMG(H))2] [X = 3-(methylthio)-1-propoxide, DBP = 2,6-di-tert-butylphenoxide, and TMG(H) = 1,1,3,3-tetramethylguanidine] (1), was designed and synthesized. The complex displays a large anisotropy barrier of 432 cm-1 in the absence of a dc magnetic field benefiting from the strong interaction between the phenolate and Dy(III) ion. Ab initio calculations reveal that the most possible relaxation pathway is going through the second excited state. The terminal SMe group in the apical position furnishes the possibility of depositing it on the Au surface by the strong Au-S bond.

On the Mechanism of Anti-galvanic Metal Displacement Reaction between [Au25(SR)18]- and Metal-Thiolate Complex.

Metal displacement reaction is widely used for preparing alloy nanomaterials. In this study, the mechanism of anti-galvanic metal displacement reaction between the atomic precision [Au25(SC2H4Ph)18]- cluster and the metal-thiolate complexes SR-M-SR (M = Ag, Cd, and Hg) is studied based on dispersion correction density functional theory (DFT-D) calculations. The present study reveals that the metal displacement reaction of the Au25 cluster is carried out through two-stage metal diffusion including the rapid diffusion of the metal heteroatom from metal thiolate to the ligand layer of Au25 cluster and then gradual diffusion of the metal heteroatom into the icosahedral 13-atom core. The atomic charge analysis confirms that the SR group plays a crucial role. Due to the partial reducibility of SR group, it can nucleophilic attack Au atom to result in the fracture of the Au-S bond in the ligand layer and the formation of atomic vacancy on the surface of the metal core, which facilitates the metal heteroatom diffusion from the metal-SR complex to the ligand layer of gold cluster and then to the surface of gold core.

Tuberculosis detection from raw sputum samples using Au-electroplated screen-printed electrodes as E-DNA sensor.

Tuberculosis (TB) remains a leading cause of death globally, especially in underdeveloped nations. The main impediment to TB eradication is a lack of efficient diagnostic tools for disease diagnosis. In this work, label free and ultrasensitive electrochemical DNA biosensor for detecting Mycobacterium tuberculosis has been developed based on the electrodeposition of gold nanoparticles on the surface of carbon screen-printed carbon electrode (Zensors) for signal amplification. Particularly, screen-printed electrodes were modified by electrochemical deposition of Au to enhance the conductivity and facilitate the immobilization of ssDNA probes via Au-S bonds. The electrochemically modified SPEs were characterized using Scanning electron microscopy/Energy Dispersive X-Ray Analysis (SEM/EDX) and X-Ray Diffraction (XRD). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques were used to investigate the DNA hybridization between single-stranded (ssDNA) probe and target DNA (tDNA). Under the ideal conditions, DPV exhibited a correlation coefficient R2 = 0.97, when analyzed with different tDNA concentrations. The proposed DNA biosensor exhibits a good detection range from 2 to 10nm with a low detection limit of 1.91nm, as well as high selectivity that, under ideal conditions, distinguishes non-complementary DNA from perfectly matched tDNA. By eliminating the need for DNA purification, this work paves the path for creating disposable biosensors capable of detecting DNA from raw sputum samples.

A molecularly imprinted electrochemical aptasensor based on zinc oxide and co-deposited gold nanoparticles/reduced graphene oxide composite for detection of amoxicillin.

The molecularly imprinted electrochemical aptasensor was constructed based on co-deposition of zinc oxide and gold nanoparticles/reduced graphene oxide composite. Aptamer was used as a new kind of functional monomer and the aptamer-amoxicillin complex was formed by hydrogen bond. Then, the complex was fixed on the surface of the modified electrode by Au-S bond. Three-dimensional imprinted polymeric membrane was formed by electropolymerization of dopamine, and the imprinted sites with good specificity and affinity were formed after elution. Combined with the specificity of molecularly imprinted technology and the affinity of aptamer, the selective recognition of amoxicillin can be realized. Under the optimal experimental conditions, the linear range was from 10-14 to 10-8 M, and the detection limit was 3.3 × 10-15 M. The sensor exhibited satisfactory selectivity, repeatability, and stability and was successfully used for 10-9 M amoxicillin determination in real water and food samples.

A turn-on fluorescent nano-probe base on methanobactin-AuNPs for simple and efficient detection of nitrite

Nitrite ions are important markers threatening humans and environmental security. A highly selective method for rapid detection of nitrite needs to be developed. Herein, a novel and rapid fluorescence method for nitrite determination is established on the basis of diazotization-coupling reaction of methanobactin (Mb) extracted by Methylosinus trichosporium OB3b with nitrite on the fluorescence. In the presence of gold nanoparticles (AuNPs), the fluorescence of AuNPs was strongly quenched by the Mb because the sulfhydryl or amino structures on the surface of Mb could be bound to the surface of AuNPs by forming Au-S or Au-N bonds. Upon addition of nitrite, the Mb easily reacts with nitrite to form azo products in the acidic medium. Then, with the increase of nitrite concentration, the Mb-AuNPs fluorescence was gradually recovered, realizing the turn-on fluorescence sensing of nitrite. Under optimal conditions, the proposed method has a good linear relationship with nitrite concentration in the range of 0–8.0 μM and 8.0–50.0 μM, and the detection limit is 16.21 nM. In addition, satisfactory results were obtained for nitrite analysis using milk, ham sausage and leaf mustard as real samples, which demonstrated that the method as-developed would have great practical application prospects.

Inhibition of Alzheimer's Aβ1-42 Fibrillogenesis and Removal of Copper Ions by Polypeptides Modified Gold Nanoparticles.

Aggregation and fibrillation of β-amyloid peptides (Aβ) as well as accumulation of toxic metal ions have been believed to be the central events to cause Alzheimer's disease (AD). Thus, an attractive therapeutic tactic for AD is to design and synthesize inhibitors and metal chelators to prevent Aβ aggregation and chelate toxic metal ions. In this study, the polypeptide functionalized gold nanoparticles (PFGNP) were obtained by modifying polypeptides Cys-Gly-Gly-Gly-Leu-Pro-Phe-Phe-Asp (CGGGLPFFD) and Cys-Gly-Gly-Gly-Gly-Gly-His (CGGGGGH) onto gold nanoparticles through gold-sulfur bond. The inhibitory properties of PFGNP toward Aβ1-42 fibril formation was assessed by thioflavin T (ThT) fluorescence method and corroborated by atomic force microscopy analysis. The ability of PFGNP to complex copper ions was studied by electrochemical method. The experimental results reveal that PFGNP can effectively chelate copper ions and significantly inhibit the fibrillation of Aβ1-42 . Moreover, PFGNP exhibits significantly protective effect on Aβ-induced cytotoxicity toward human neuroblastoma SH-SY5Y cells.

Glass Nanopore Detection of Copper Ions in Single Cells Based on Click Chemistry.

As a common redox metal ion pair in cells, copper ions (Cu2+/Cu+) often transform between oxidation (Cu2+) and reduction (Cu+) states. They play important roles in the redox process, so monitoring the change of intracellular copper ions helps understand the redox balance and events in cells. In this study, by self-assembling a thiolated ssDNA (with an alkyne end group) onto a gold-coated glass nanopore (G-nanopore) via the Au-S bond, an alkyne-end single-stranded DNA (ssDNA)-functionalized G-nanopore sensing platform (AG-nanopore) was developed to detect copper ions in cells. In the presence of Cu2+ or Cu+, the introduction of another ssDNA with an azide group will be ligated with an alkyne group on the functionalized nanopore via a copper-catalyzed azide-alkyne 1,3-cycloaddition (CuAAC) click reaction and hence cause the change of the rectification behavior of the AG-nanopore. The rectification ratio variation of the AG-nanopore had a good response to the intracellular copper ion concentration, and the sensing platform was further applied to the study of the relationship between intracellular oxidative stress and the value of Cu2+/Cu+.

Electrochemiluminescence biosensor for carcinoembryonic antigen detection based on Au-Ag/g-C3N4 nanocomposites

Herein, an electrochemiluminescence (ECL) aptasensor for carcinoembryonic antigen (CEA) detection was developed based on Au-Ag/g-C3N4 nanocomposites (NCs), which were synthesized by decorating graphitic carbon nitride (g-C3N4) nanosheets with alloy-structured Au-Ag bimetallic nanoparticles (NPs) via one-step in situ chemical reduction. As ECL sensing platform, Au-Ag/g-C3N4 NCs could significantly improve the ECL intensity of luminol due to the good conductivity of Au-Ag NPs, electrocatalytic activity for oxygen evolution reaction (OER) and the ability to adsorb luminol via π stacking interaction. In addition, it could load the thiol terminated aptamers of CEA via Au-S or Ag-S bonds. In the presence of CEA, the ECL response of the proposed biosensor decreased significantly due to the fact that the assembled protein layers hindered the electron transfer and the diffusion of ECL reactants toward the electrode surface. The proposed ECL sensor exhibited a good linear relationship with CEA in the range of 1.0–1.0 × 10−6 ng/mL with a detection limit of 8.9 × 10−7 ng/mL. The satisfactory results were obtained in the detection of CEA in human serum samples.

Bifunctional Magnetic Fe3O4@Cu2O@TiO2 Nanosphere-Mediated Dual-Mode Assay of PTP1B Activity Based on Photocurrent Polarity Switching and Nanozyme-Engineered Biocatalytic Precipitation Strategies.

Dysregulation of protein phosphatases is associated with the progression of various human diseases and cancers. Herein, a photoelectrochemical (PEC)-quartz crystal microbalance (QCM) dual-mode sensing platform was developed for protein tyrosine phosphatase 1B (PTP1B) activity assay based on bifunctional magnetic Fe3O4@Cu2O@TiO2 nanosphere-mediated PEC photocurrent polarity switching and QCM signal amplification strategies. The PTP1B-specific phosphopeptide (P-peptide) with a cysteine end was designed and immobilized onto the QCM Au chip via the Au-S bond. Subsequently, the Fe3O4@Cu2O@TiO2 nanosphere was connected to the P-peptide via the specific interaction between the phosphate group on the P-peptide and TiO2. After incubation with PTP1B, the dephosphorylation of the P-peptide occurred, causing some Fe3O4@Cu2O@TiO2 nanospheres to be released from the chip surface. The released magnetic Fe3O4@Cu2O@TiO2 nanospheres (labeled as R-Fe3O4@Cu2O@TiO2) were quickly separated via magnetic separation technology and attached to the Bi2S3-decorated magnetic indium-tin oxide (Bi2S3/MITO) electrode by magnetic force, inducing the switch of the photocurrent polarity of the electrode from anodic current (the Bi2S3/MITO electrode) to cathodic current (the R-Fe3O4@Cu2O@TiO2/Bi2S3/MITO electrode). Also, the nondephosphorylated P-peptide linked Fe3O4@Cu2O@TiO2 nanospheres as nanozymes with horseradish peroxidase activity to catalyze the formation of precipitation on the surface of the Au chip, leading to a frequency change of the QCM. Thus, the proposed PEC-QCM dual-mode sensing platform achieved accurate and reliable assay of PTP1B activity because of the different mechanisms and independent signal transductions. In addition, this dual-mode sensing platform can be easily extended for other protein phosphatase activity analysis and shows great potential in the early diagnosis of the protein phosphatase-related diseases and the protein phosphatase-targeted drug discovery.

Highly Sensitive Photoelectrochemical Biosensor for MicroRNA-21 Based on a Dumbbell-Shaped Heterostructure AuNRs@end-TiO2 Combined with Carbon Dots as Photosensitizers and Duplex-Specific Nuclease-Assisted Signal Amplification.

TiO2 was grown on both ends of gold nanorods (AuNRs) to form a dumbbell-shaped heterostructure (called AuNRs@end-TiO2) first, and then assembled on the fluorine tin oxide (FTO) electrode surface through hydrophobic interactions to construct a concise photoelectrochemical microRNA-21 (miRNA-21, model target) biosensor using carbon dots (CDs) as photosensitizers. Hairpin probes (HPs) were fixed on the AuNRs@end-TiO2-modified FTO electrode surface through the Au-S bond, and CDs-modified complementary DNA (CDs-cDNA) served as photosensitive probes. In the presence of the target, miRNA hybridized with the HP and triggered double-strand-specific nuclease to cleave the complementary part of the HP with miRNA, and miRNA was released, which can trigger another cycle to realize signal amplification. Many HPs were cleaved and the complementary sequence with cDNA was exposed, which can capture the photosensitive probes to the electrode surface and resulted in photocurrent enhancement. The photocurrent intensity system has a linear relationship with the logarithm of the miRNA concentration in the range of 0.1 fM to 100 pM with a low detection limit of 96 aM (S/N = 3). The biosensor has high sensitivity, good selectivity, and good reproducibility and shows satisfactory results in actual sample detection.

Ultrastable water-dispersible one-dimensional gold nanoparticles@cellulose nanocrystal

Cellulose nanocrystals (CNCs) with high aspect ratio, ultrafine template structure and surface modifiability were used as the multifunctional support to fabricate one dimensional (1D) nanoprobe based on surface-enhanced Raman scattering spectroscopy (SERS) technology. Quaternary ammonium groups were first introduced at the hydroxyl sites on the surface of CNCs to improve the dispersion stability in aqueous solution, and then sulfhydryl groups were conjugated to the carboxyl sites through amidation. Gold nanospheres (AuNSs) were self-assembled on CNCs via strong Au-S bonds to form dense hot spots, which can easily distinguish the rhodamine (R6G) signal of six orders of magnitude when used as a SERS probe. Because the hot spots are fixed along a single CNC, the SERS signal stability and reproducibility are greatly improved compared to those of changeable hot spots formed via the irreversible aggregation of gold colloids. In addition, owing to the cationic charge repulsion effect, the nanoprobe exhibits excellent dispersion stability even in high concentration salt solutions. Considering the good sensitivity, reproducibility and dispersibility, the 1D SERS nanoprobe based on CNCs possess potential application in the field of sensing and detection in aqueous solutions.

Ultrastable gold nanoparticles-based nanoplatform with mitochondria targeting and high-fidelity intracellular bioimaging enterokinase levels

Mitochondria are key organelles in mammalian cells whose dysfunctions are linked to various diseases. Numerous gold nanoparticles functionalized with lipophilic cation categories via Au-S bond for mitochondria targeting have been reported. However, cleavage of the Au-S bond by biothiols and other chemicals is a long-standing problem hindering practical applications, especially for intracellular detection and bioimaging. Herein, we report a mitochondria-targeting AuNP-based nanosensor with negatively charged peptide modification. Furthermore, we directly introduce the peptide motif via diselenide-modified AuNPs instead of traditional Au-S bonds. In vitro and living cell-based assays show that our designed strategy is simple to prepare, but ultrastable under thiol-rich physiological conditions. Furthermore, we have demonstrated that the nanosensor AuNP@DSe-PlinkerTMR can monitor enterokinase (ENTK) levels in the mitochondria of HeLa cells with a high-fidelity fluorescent signal under physiological conditions, thus providing a new idea for the design and preparation of ultrastable AuNP-based nanosystem.

On the role of alkanethiol Au complex in the formation of gold deposits; an in-silico approach

The association of organic matter with ore minerals has been observed for many years. Over decades, many speculations have been proposed to define the possible roles that organic matter might have played in the ore genesis. In this paper, we performed a series of electronic calculations, and molecular dynamic simulations to investigate the behaviour of organic matter in ore-forming environments.Ab initio calculations revealed that variation in the length of alkane tails has a limited impact on the geometry of the Au-ligand, and the strength of AuS bonds. MD and metadynamics simulations proved that the organic Au-ligand could be dissolved in the organic phase but it mostly pose at the interface of the organic-inorganic phase, in a way that its ionic head place in the aqueous solution and its alkane tails dissolved in organic matter. These observations suggest the organic-gold ions (and organic ligands of some other metals) are preferentially accumulated in the narrow interface of the aqueous/petroleum phase. Overall, although experimental results suggest that organic matter might have a role in gold transport, this study proves that organic gold ligand is concentrated only at the interface between the organic and aqueous phases and therefor, the organic phase alone cannot carry gold. This finding is also consistent with field observations, which suggest that gold concentrations in oil are relatively low.

Dual-modal biosensor for highly sensitive and selective DNA methyltransferase activity detection based on a porous organic polymer-inorganic nanocomposite (Cu2O@FePPOPBADE) with high laccase-like activity

Abnormal DNA Methyltransferase (MTase) activity is closely related with multiple human diseases, which triggered its accurate and sensitive detecting demands. Here, an electrochemical and colorimetric, dual-modal biosensor for Dam MTase (Dam) assay was developed based on an organic-inorganic nanocomposite (Cu2O@FePPOPBADE). Stemming from the laccase-like activity of Cu2O, the catalytic activity of ferriporphyrin and excellent protective effect of the FePPOPBADE shell, Cu2O@FePPOPBADE not only exhibited significantly improved laccase-like activity to catalyze the chromogenic reaction of 2,4-dichlorophenol (2,4-DP) with 4-aminoantipyrine (4-AP), but possessed a strong electrochemical signal. Cu2O@FePPOPBADE was further functionalize with Au nanoparticles and served as a signal probe (Cu2O@FePPOPBADE@AuNPs). Also, magnetic bead (MB)/dsDNA was designed by assembly of streptavidin-modified MB with biotinylated-terminated ssDNA1 and thiolated-terminated ssDNA2, both of which contained specific sequences 5′-G-A-T-C-3′. When Dam and Dpn I were present, the specific sequence of dsDNA is methylated by Dam and then is cut by Dpn I, causing the leaving of thiolated-terminated ssDNA2. Sequentially, the residual MB/dsDNA is linked to the Cu2O@FePPOPBADE@AuNPs probe via Au-S bonds. After another magnetic separation, the unlinked Cu2O@FePPOPBADE@AuNPs left in the supernatant were transferred to accomplish the “dual signal-on” analysis of Dam with lower detection limits and high specificity.

Real-Time Tracking of Electrical Signals and an Accurate Quantification of Chemical Signals with Long-Term Stability in the Live Brain.

The development of in vivo analytical tools and methods for recording electrical signals and accurately quantifying chemical signals is a key issue for a comprehensive understanding of brain events. The electrophysiological microelectrode was invented to monitor electrical signals in free-moving brains. On the other hand, electrochemical assays with excellent spatiotemporal resolution provide an effect way to monitor chemical signals in vivo. Unfortunately, the in vivo electrochemical biosensors still have three limitations. First, many biological species such as reactive oxygen species (ROS) and neurotransmitters demonstrate large overpotentials at conventional electrodes. Thus, it is hard to convert the chemical/electrochemical signals of these molecules into electric signals. Second, the interfacial properties of the recognition molecules assembled onto the electrode surfaces have a great influence on the transmission of electric charge through the interface and the stability of the modified recognition molecules. Meanwhile, the surface of biosensors implanted in the brain is easily absorbed by many proteins present in the brain, resulting in the loss of signals. Finally, activities in the brain including neuron discharges and electrophysiological signals may be affected by electrochemical measurements due to the application of extra potentials and/or currents.This Account presents a deep view of the fundamental design principles and solutions in response to the above challenges for developing in vivo biosensors with high performance while meeting the growing requirements, including high selectivity, long-time stability, and simultaneously monitoring electrical and chemical signals. We aim to highlight the basic criteria based on a double-recognition strategy for the selective biosensing of ROS, H2S, and HnS through the rational design of specific recognition molecules followed by electrochemical oxidation or reduction. Recent developments in designing functionalized surfaces through a systematic investigation of self-assembly with Au-S bonds, Au-Se bonds, and Au≡C bonds for facilitating electrochemical properties as well as improving the stability are summarized. More importantly, this Account highlights the novel methodologies for simultaneously monitoring electrical and chemical signals ascribed to the dynamic changes in K+, Na+, and Ca2+ and pH values in vivo. Additionally, SERS-based photophysiological microarray probes have been developed for quantitatively tracking chemical changes in the live brain together with recording electrophysiological signals.The design principles and novel strategies presented in this Account can be extended to the real-time tracking of electrical signals and the accurate quantification of more chemical signals such as amino acids, neurotransmitters, and proteins to understand the brain events. The final part also outlines potential future directions in constructing high-density microarrays, eventually enabling the large-scale dynamic recording of the chemical expression of multineuronal signals across the whole brain. There is still room to develop a multifiber microarray which can be coupled with photometric methods to record chemical signals both inside and outside neurons in the live brains of freely moving animals to understand physiological processes and screen drugs.