Design and green synthesis of carbon Dots/Gold nanoparticles Composites and their applications for neurotransmitters sensing based on emission Spectroscopy

Changes in the neurotransmitters are indications for several diseases. Several sensors were reported for monitoring dopamine (DA), but the simple and accurate DA detection in biological samples still faces many challenges. The research proposal aims to develop an optical sensor for detecting neurotransmitters based on luminescence emission spectra in different biological samples. Carbon dots (CDs) were fabricated based on a green synthesis route. Then the prepared CDs were decorated with varying concentrations of gold nanoparticles (Au NPs). The synthesis process was optimized, and the obtained CDs/Au NPs nanocomposites were applied as neurotransmitters' optical nanosensors. The optical nanosensor approach provides easy and sensitive multiplex analysis. A wide range of neurotransmitters was monitored. The developed sensor's sensitivity, selectivity, and reproducibility were investigated. Au NPs act as CDs' stabilizers, enhancing the emission effect, and scaffolds for binding DA with CDs' surface. DA moieties bind to CDs through the interaction between the DA-NH2 groups and Au NPS. Due to electron transfer, the bonding of DA molecules leads to fluorescence quenching of AuNPs/CDs. The Au-CDs-based DA fluorescence showed high sensitivity with adetection limit, and limit quantification of 2.04 nM and 6.18 nM, respectively. Furthermore, the selectivity of the sensor was investigated in the presence of glucose, uric acid (UA), and ascorbic acid (AA), which showed no interference effect at 10 times higher concentrations. Moreover, the proposed sensor has been successfully utilized for DA detection in human serum samples with a high recovery efficiency between 98.83 % and 103.5 %.

Visual Detection of Dopamine with CdS/ZnS Quantum Dots Bearing by ZIF-8 and Nanofiber Membranes

Dopamine (DA) is a widely present, calcium cholinergic neurotransmitter in the body, playing important roles in the central nervous system and cardiovascular system. Developing fast and sensitive DA detection methods is of great significance. Fluorescence-based methods have attracted much attention due to their advantages of easy operation, a fast response speed, and high sensitivity. This study prepared hydrophilic and high-performance CdS/ZnS quantum dots (QDs) for DA detection. The waterborne CdS/ZnS QDs were synthesized in one step using the amphiphilic polymer PEI-g-C14, obtained by grafting tetradecane (C14) to polyethyleneimine (PEI), as a template. The polyacrylonitrile nanofiber membrane (PAN-NFM) was prepared by electrospinning (e-spinning), and a metal organic frame (ZIF-8) was deposited in situ on the surface of the PAN-NFM. The CdS/ZnS QDs were loaded onto this substrate (ZIF-8@PAN-NFM). The results showed that after the deposition of ZIF-8, the water contact angle of the hydrophobic PAN-NFM decreased to within 40°. The nanofiber membrane loaded with QDs also exhibited significant changes in fluorescence in the presence of DA at different concentrations, which could be applied as a fast detection method of DA with high sensitivity. Meanwhile, the fluorescence on this PAN-NFM could be visually observed as it transitioned from a blue-green color to colorless, making it suitable for the real-time detection of DA.

A ratiometric fluorescence sensor based on the inner filtration effect of gold nanoparticles on quantum dots for monitoring dopamine

In this study, a smart phone assisted ratiometric fluorescence sensor was designed for detecting dopamine (DA). The ratiometric fluorescence sensor was prepared by simple physical mixing green quantum dots (GQDS) and red quantum dots (RQDS). DA could induce gold nanoparticles (AuNPs) aggregate via hydrogen-bonding interactions, and further changed the absorption spectrum of gold nanoparticles to overlap with a certain emission spectrum of ratiometric fluorescence sensor. AuNPs had inner filtration effect (IFE) on the ratiometric fluorescence sensor. Due to the IFE, the dispersive AuNPs could quench GQDS, whereas the clustered AuNPs could quench RQDS. With the addition of DA, the color of ratiometric fluorescence changed from orange red to green. To simplify the detection process, a smartphone was employed to detecting DA in human urine by measuring RGB value of fluorescence color changes with a detection limit of 86 nM. This proposed method has the advantages of low cost, easy prevalence and simple operation, thus provides a great promise for rapid detection of biomarker in biological samples.

A photoluminescence sensor for in-situ monitoring of the dopamine neurotransmitters released from PC12 cells

Constructing simple, stable, fast, and sensitive neurotransmitter-based sensors is a promising tool to diagnose neurological diseases. Dopamine (DA), "a catecholamine neurotransmitter" is important in transmitting nerve impulses. Therefore, great attention is taken to monitor DA concentrations received. The challenge in developing a DA-based sensor is to enhance its stability and sensitivity. Thus, we have used o-phthalaldehyde (OPA)/2-mercapto ethanol (2ME)/mesoporous silica instated of 2ME in solution. Here we have successfully developed a fluorescence DA neurotransmitters sensor. The sensor was used for detecting a wide range of concentrations of DA (5 nM to 5 µM). Effects of pH (4.3-11.4) and temperatures (25-70 °C) on the sensor efficiency were investigated. The detection limit was 1.35 × 10^-11 mol/dm³, which is lower than the normal DA level in the central nervous system. The results indicated that using OPA/2ME/MSNPs has long-time stability over a year of its preparation. Moreover, the developed sensor showed high specificity towards DA in the presence of different interferences such as ascorbic acid or another catecholamine neurotransmitter such as γ-aminobutyric acid. Finally, the fabricated biosensor was used to monitor the DA neurotransmitter released from PC12 cells. Hence, it was successfully developed a simple and stable probe for accurate photoluminescence detection of DA neurotransmitters.

Influence of the Co-Adsorbed Ions on the Surface-Enhanced Raman Scattering Spectra of Dopamine Adsorbed on Nanostructured Silver

The abnormal metabolism or imbalance of dopamine may lead to some neurological disorders. Therefore, the facile and fast detection of this neurotransmitter is essential in the early diagnosis of some diseases. One of the methods that can be used for the detection and determination of dopamine is the surface-enhanced Raman scattering (SERS). In this contribution, we report a very strong influence of some salts (we used salts containing Na⁺ cations and the following anions: SO₄^2-, F^-, Cl^-, Br^-, and I^-) on the spectral patterns and intensity of the SERS spectra of dopamine adsorbed on a nanostructured macroscopic silver substrate. The analysis of the recorded SERS spectra based on the assignments of Raman bands from the density-functional theory (DFT) calculations and based on the SERS surface selection rules reveals that when molecules of dopamine are adsorbed from an aqueous solution to which no electrolytes have been added, they adopt a flat orientation versus the silver surface; whereas, the molecules of dopamine co-adsorbed with various ions interact with the silver surface, mainly via phenolic groups, and they adopt a perpendicular orientation versus the metal surface. An addition of electrolytes also significantly influences the intensity of the recorded SERS spectrum; for example, an addition of Na₂SO₄ to a final concentration of 1 M induces an increase in the intensity of the measured SERS spectrum by a factor of ca. 40. This means that the addition of electrolytes to the analyzed solution can reduce the limit of detection of dopamine by SERS spectroscopy. The abovementioned findings may facilitate the construction of dopamine SERS sensors.

Rosaniline Hydrochloride Encapsulated MCM-48: Fluorescent and Electrochemical Sensor for Dopamine

The dye Rosaniline hydrochloride (RANH) has been successfully incorporated in MCM-48 (designated as RANH@MCM-48) and characterized by various spectroscopic methods including FT-IR, SEM, EDX and N₂ adsorption-desorption isotherm. RANH@MCM-48 in aqueous medium acts as fluorescence "on" sensor for neurotransmitter dopamine (DA) in presence of its main biological interfering agent ascorbic acid or vitamin c (AA) along with Glucose, Cholesterol and Uric acid (UA). The limits of detection (LOD) were found to be 65 nM and 51 nM respectively in absence and in presence of AA. The interaction of DA to RANH@MCM-48 is found to be reversible with respect to EDTA^2-. The fluorescence intensity vs. pH plot shows a narrow fluorescence window of 7.2 to 8.8. RANH@MCM-48 has been successfully applied for DA detection in artificial cerebrospinal fluid (ACF) and bovine serum albumin (BSA) with LOD values 27 nM and 22.5 nM respectively. Platinum disc electrode has been modified with RANH@MCM-48 which showed distinct oxidation peaks with a separation of 0.188 V in cyclic voltammetry (CV). The LOD for DA in presence of AA determined from oxidation current is 77.5 nM. The voltammetric detection of DA is found to be free from common interfering species Na⁺, K⁺, Ca²⁺, Fe²⁺, UA, Cholesterol and Glucose. RANH@MCM-48 has been found to be a very effective fluorescence and voltammetric sensor for DA with very low  LOD.

Nanoparticle-based colorimetric sensors to detect neurodegenerative disease biomarkers

Neurodegenerative disorders (NDDs) are progressive, incurable health conditions that primarily affect brain cells, and result in loss of brain mass and impaired function. Current sensing technologies for NDD detection are limited by high cost, long sample preparation, and/or require skilled personnel. To overcome these limitations, optical sensors, specifically colorimetric sensors, have garnered increasing attention towards the development of a cost-effective, simple, and rapid alternative approach. In this review, we evaluate colorimetric sensing strategies of NDD biomarkers (e.g. proteins, neurotransmitters, bio-thiols, and sulfide), address the limitations and challenges of optical sensor technologies, and provide our outlook on the future of this field.

Turn-on fluorescent probe for dopamine detection in solutions and live cells based on in situ formation of aminosilane-functionalized carbon dots

Dopamine (DA) is a critical biomarker for a variety of neurological diseases. Methods for simple and rapid DA detection are crucial for clinical diagnosis and treatments for those diseases. In this work, we developed a novel pretreatment-free method for dopamine detection using carbon dots as a turn-on fluorescent probe synthesized in situ. The aminosilane-functionalized carbon dots (SiCDs) were produced in a mild condensation reaction between N-[3-(Trimethoxysilyl)propyl]ethylenediamine (AEATMS) and dopamine, which were directly used for probing of dopamine. The prepared SiCDs exhibited green fluorescence with excitation/emission maximum at 380/495 nm, the intensity of which can be measured to quantify the DA present in the reaction mixture. The linear range of the assay was between 0.1 and 100 μM with a limit of detection (LOD) of 56.2 nM. The probe is of good selectivity and the recoveries of the developed method were in the range of 101.77-119.91% with RSDs within 3.67% in human serum sample tests. The SiCDs were also synthesized within MN9D cells under 37 °C and generated bright fluorescence, which can probe the DA's distribution in the cells. The described method exhibit potential in DA detection and live-cell imaging for its feature of facility, inexpensiveness, and sensitivity.

Hemin-doped metal-organic frameworks based nanozyme electrochemical sensor with high stability and sensitivity for dopamine detection

This study reports a new type of artificial nanozyme based on Hemin-doped-HKUST-1 (HKUST-1, also referred to as MOF-199; a face-centered-cubic MOF containing nanochannels) as a redox mediator for the detection of dopamine (DA). Hemin-doped-HKUST-1 was successfully synthesized by one-pot hydrothermal method, which was combined with reduced graphene oxide (rGO) modified on a glassy carbon electrode (GCE) to construct a sensor (Hemin-doped HKUST-1/rGO/GCE). The morphology and structure of Hemin-doped-HKUST-1 were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and infrared spectra (IR) techniques. The Hemin-doped HKUST-1/rGO nanozyme showed an excellent electrocatalytic activity for DA oxidation, which is due to the enhanced Hemin activity through the formation of a metal-organic framework (MOFs) and the synergy between the Hemin-doped HKUST-1 and rGO in nanozyme. The resulted sensor exhibited a high sensitivity of 1.224 μA μM-1, with a lower detection limit of 3.27 × 10-8 M (S/N = 3) and a wide linear range of 0.03-10 μM for DA detection. In addition, due to the stabilizing effect of MOFs on heme, the sensor showed satisfactory stability and has been successfully applied to the detection of DA in serum samples, indicating that this work has potential value in clinical work.

A sensitive method to determine dopamine in the presence of uric acid based on In2O3 nanosheet arrays grown on 3D graphene

A nonenzymatic voltammetric assay for dopamine (DA) was developed based on the combination of three-dimensional graphene (3D Gr) and indium oxide nanosheet arrays (In₂O₃ NSAs). 3D Gr was prepared by chemical vapor deposition (CVD), and In₂O₃ NSAs were grown on its surface by hydrothermal synthesis. The results show that 3D Gr maintains a good porous structure (200 μm), and the pore size of In₂O₃ NSAs is 0.50 μm. Differential pulse voltammetry (DPV) is mainly used to determine the electrochemical properties of In₂O₃ NSAs/3D Gr. It possesses a sensitivity of 2.69 μA·μM^-1·cm^-2 towards DA (5-60 μM) at 0.14 V, and the detection limit (LOD) is 0.10 μM (S/N = 3). The recoveries obtained for spiked samples in the real sample detection is 105 (± 8)%. Graphical abstractSchematic representation of DA sensitive detection by growing In₂O₃ nanosheets arrays on three-dimentional graphene modified ITO.

Recent Advances in Electrochemical and Optical Sensing of Dopamine

Nowadays, several neurological disorders and neurocrine tumours are associated with dopamine (DA) concentrations in various biological fluids. Highly accurate and ultrasensitive detection of DA levels in different biological samples in real-time can change and improve the quality of a patient's life in addition to reducing the treatment cost. Therefore, the design and development of diagnostic tool for in vivo and in vitro monitoring of DA is of considerable clinical and pharmacological importance. In recent decades, a large number of techniques have been established for DA detection, including chromatography coupled to mass spectrometry, spectroscopic approaches, and electrochemical (EC) methods. These methods are effective, but most of them still have some drawbacks such as consuming time, effort, and money. Added to that, sometimes they need complex procedures to obtain good sensitivity and suffer from low selectivity due to interference from other biological species such as uric acid (UA) and ascorbic acid (AA). Advanced materials can offer remarkable opportunities to overcome drawbacks in conventional DA sensors. This review aims to explain challenges related to DA detection using different techniques, and to summarize and highlight recent advancements in materials used and approaches applied for several sensor surface modification for the monitoring of DA. Also, it focuses on the analytical features of the EC and optical-based sensing techniques available.

Sensitive and selective colorimetric probe for fluoride detection based on the interaction between 3-aminophenylboronic acid and dithiobis(succinimidylpropionate) modified gold nanoparticles

APBA was conjugated on DSP@AuNP to form stable APBA–DSP@AuNP, exhibiting high selectivity towards fluoride against other anions and glucose.

CdTe0.5S0.5/ZnS Quantum Dots Embedded in a Molecularly Imprinted Polymer for the Selective Optosensing of Dopamine

This work describes the preparation of molecularly imprinted polymer (MIP)-modified core/shell CdTe_0.5S_0.5/ZnS quantum dots (QDs). The QDs@MIP particles were used for the selective and sensitive detection of dopamine (DA). Acrylamide, which is able to form hydrogen bonds with DA, and ethylene glycol dimethylacrylate (EGDMA) as cross-linker were used for the preparation of the MIP. Highly cross-linked polymer particles with sizes up to 1 µm containing the dots were obtained after the polymerization. After the removal of the DA template, MIP-modified QDs (QDs@MIP) exhibit a high photoluminescence (PL) with an intensity similar to that of QDs embedded in the nonimprinted polymer (NIP). A linear PL decrease was observed upon addition of DA to QDs@MIP and the PL response was in the linear ranges from 2.63 µM to 26.30 µM with a limit of detection of 6.6 nM. The PL intensity of QDs@MIP was quenched selectively by DA. The QDs@MIP particles developed in this work are easily prepared and of low cost and are therefore of high interest for the sensitive and selective detection of DA in biological samples.

Metal–oxygen clusters as peroxidase mimics for their multifarious applications in colorimetric sensors

Metal–oxygen cluster (Fe₂₈) was certified to own inherent peroxidase-like performance, which displayed multi-functional applications in H₂O₂, glucose and dopamine detection.

A novel calix[4]arene-modified porphyrin-based dual-mode sensor for the specific detection of dopamine with excellent performance

A dual-mode sensor for dopamine with remarkable specificity is developed based on a novel calix[4]arene-functionalized porphyrin derivative.

Reliable and quantitative SERS detection of dopamine levels in human blood plasma using a plasmonic Au/Ag nanocluster substrate

Accurate and rapid blood-based detection of dopamine levels can aid in the diagnosis and monitoring of diseases related to dopaminergic dysfunction. For the sensitive detection of dopamine levels in human blood plasma (i.e., plasma dopamine levels), a silver-plated Au bimetallic nanocluster (so called plasmonic Au/Ag nanocluster) was prepared as a surface-enhanced Raman scattering (SERS) substrate by the combination of electrodeposition and electroless plating methods. The plasmonic effect of the Au/Ag nanocluster substrate was optimized by controlling the particle morphology, packing density, and interparticle distance, showing the best performance in its SERS activity. The lowest detection limit of dopamine was ∼10^-11 M. A linear standard curve was obtained by plotting the log-scale of dopamine concentration (log C) versus Raman intensity at 1152 cm^-1. The optimized SERS substrate quantified the plasma dopamine levels of patients with antipsychotic drug-induced Parkinsonism (n = 15) as 3.24 × 10^-9 M and healthy control subjects (n = 15) as 2.31 × 10^-8 M. Patients with drug-induced Parkinsonism had ∼86% lower plasma dopamine concentration than healthy subjects (two-tailed p-value = 0.000002), indicating a clear separation between the groups. Our study provides the first report on the quantitative SERS detection of dopamine levels in human blood plasma with Parkinsonism. The results highlight the potential clinical utility of the optimized SERS technique in screening clinical populations with dopaminergic dysfunction, i.e., differentiating between healthy subjects and patients with Parkinsonism.

A fluorescent sensor based on thioglycolic acid capped cadmium sulfide quantum dots for the determination of dopamine

A fluorescent sensor based on thioglycolic acid-capped cadmium sulfide quantum dots (TGA-CdS QDs) has been designed for the sensitive and selective detection of dopamine (DA). In the presence of dopamine (DA), the addition of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) activates the reaction between the carboxylic group of the TGA and the amino group of dopamine to form an amide bond, quenching the fluorescence of the QDs. The fluorescence intensity of TGA-CdS QDs can be used to sense the presence of dopamine with a limit of detection of 0.68μM and a working linear range of 1.0-17.5μM. This sensor system shows great potential application for dopamine detection in dopamine drug samples and for future easy-to-make analytical devices.

Nanostructured carbon electrode modified with N-doped graphene quantum dots-chitosan nanocomposite: a sensitive electrochemical dopamine sensor

A highly selective and sensitive dopamine electrochemical sensor based on nitrogen-doped graphene quantum dots-chitosan nanocomposite-modified nanostructured screen printed carbon electrode is presented, for the first time. Graphene quantum dots were prepared via microwave-assisted hydrothermal reaction of glucose, and nitrogen doping was realized by introducing ammonia in the reaction mixture. Chitosan incorporation played a significant role towards the selectivity of the prepared sensor by hindering the ascorbic acid interference and enlarging the peak potential separation between dopamine and uric acid. The proposed sensor's performance was shown to be superior to several recently reported investigations. The as-prepared CS/N,GQDs@SPCE exhibited a high sensitivity (i.e. ca. 418 µA mM cm^-2), a wide linear range i.e. (1-100 µM) and (100-200 µM) with excellent correlations (i.e. R² = 0.999 and R² = 1.000, respectively) and very low limit of detection (LOD = 0.145 µM) and limit of quantification (LOQ = 0.482 µM) based on S/N = 3 and 10, respectively. The applicability of the prepared sensor for real sample analysis was tested by the determination of dopamine in human urine in pH 7.0 PBS showing an approximately 100% recovery with RSD < 2% inferring both the practicability and reliability of CS/N,GQDs@SPCE. The proposed sensor is endowed with high reproducibility (i.e. RSD = ca. 3.61%), excellent repeatability (i.e. ca. 0.91% current change) and a long-term stability (i.e. ca. 94.5% retained activity).

Unique Roles of Gold Nanoparticles in Drug Delivery, Targeting and Imaging Applications

Nanotechnology has become more and more potentially used in diagnosis or treatment of diseases. Advances in nanotechnology have led to new and improved nanomaterials in biomedical applications. Common nanomaterials applicable in biomedical applications include liposomes, polymeric micelles, graphene, carbon nanotubes, quantum dots, ferroferric oxide nanoparticles, gold nanoparticles (Au NPs), and so on. Among them, Au NPs have been considered as the most interesting nanomaterial because of its unique optical, electronic, sensing and biochemical properties. Au NPs have been potentially applied for medical imaging, drug delivery, and tumor therapy in the early detection, diagnosis, and treatment of diseases. This review focuses on some recent advances in the use of Au NPs as drug carriers for the intracellular delivery of therapeutics and as molecular nanoprobes for the detection and monitoring of target molecules.

Gold Nanoparticle-Based Colorimetric and Electrochemical Methods for Dipeptidyl Peptidase-IV Activity Assay and Inhibitor Screening

We presented the colorimetric and electrochemical methods for determination of the dipeptidyl peptidase-IV (DPP-IV) activity and screening of its inhibitor using gold nanoparticle (AuNP) as the probe. In the colorimetric assay, the substrate peptide with a sequence of Arg-Pro-Arg induced the aggregation and color change of AuNPs, whereas cleavage of the peptide by DPP-IV prevented the aggregation of AuNPs. Furthermore, the aggregation of AuNPs in the solution was easily initiated on a solid/liquid (electrode/electrolyte) surface, which induced a decrease in the electron-transfer resistance. However, once the peptide was clipped by DPP-IV, the assembly of AuNPs on electrode surface was prevented. Consequently, a higher electron-transfer resistance was observed. The colorimetric and electrochemical assays allowed for the determination of DPP-IV with the detection limits of 70 μU/mL and 0.55 μU/mL, respectively. Meanwhile, the proposed methods were used to determine DPP-IV inhibitor with satisfactory results. Both the colorimetric and electrochemical methods are simple, rapid and sufficiently sensitive for DPP-IV activity assay and inhibitor screening. The results also demonstrated that the AuNP-based colorimetric assay could be converted into an enhanced surface tethered electrochemical assay with improving sensitivity. The simple detection principle may be extended to the design of other peptidases biosensors with easy manipulation procedures.

Simple and Sensitive Colorimetric Detection of Dopamine Based on Assembly of Cyclodextrin-Modified Au Nanoparticles

A controlled assembly of natural beta-cyclodextrin modified Au NPs mediated by dopamine is demonstrated. Furthermore, a simple and sensitive colorimetric detection for dopamine is established by the concentration-dependent assembly.

Construction of Plasmonic Core-Satellite Nanostructures on Substrates Based on DNA-Directed Self-Assembly as a Sensitive and Reproducible Biosensor

We report the successful construction of plasmonic core-satellite nanostructured assemblies on two-dimensional substrates, based on a strategy of combining DNA-functionalized plasmonic nanoparticles (NPs) with the specific recognition ability toward target to enable satellite NPs to self-assemble around the core immobilized on substrates. A strongly coupled plasmonic resonance band was observed because of the close proximity between core and satellite NPs, which presented significant red-shift and enhanced extinction with respect to the local surface plasmon resonance (LSPR) band of individual core NPs on the substrate. The functionality of this core-satellite nanostructured assembly as a biosensor was further explored, and the changes in extinction intensity and the peak shift of the plasmonic coupling resonance band arising from the probe-target DNA binding event all proved to be useful criteria for target DNA detection. Moreover, high selectivity down to single-base mismatched DNA was achieved using this strongly coupled plasmonic core-satellite nanostructured assembly on a substrate. Such substrate-based detection was advantageous, and its reusability and high cycle stability were demonstrated after five cycles of disassembly and reassembly. Our work demonstrates the biosensing capacity of this DNA-functionalized plasmonic nanoassembly model system on two-dimensional substrate, which is also applicable to the detection of numerous DNA-recognized biomolecules. Likewise, the presented construction method can be extended to fabricate other compositional core-satellite nanoassemblies.

Selective detection of dopamine in the presence of ascorbic acid via fluorescence quenching of InP/ZnS quantum dots

Dopamine is a neurotransmitter of the catecholamine family and has many important roles, especially in human brain. Several diseases of the nervous system, such as Parkinson’s disease, attention deficit hyperactivity disorder, restless legs syndrome, are believed to be related to deficiency of dopamine. Several studies have been performed to detect dopamine by using electrochemical analysis. In this study, quantum dots (QDs) were used as sensing media for the detection of dopamine. The surface of the QDs was modified with l-cysteine by coupling reaction to increase the selectivity of dopamine. The fluorescence of cysteine-capped indium phosphide/zinc sulfide QDs was quenched by dopamine with various concentrations in the presence of ascorbic acid. This method shows good selectivity for dopamine detection, and the detection limit was 5 nM.

Silver nanoparticles-enhanced rare earth co-luminescence effect of Tb(III)-Y(III)-dopamine system

It was found that silver nanoparticles (AgNPs) could enhance co-luminescence effect of rare earths ions Tb(3+) and Y(3+). Based on this, a sensitive fluorescence detection method for the determination of dopamine (DA) was proposed. Moreover, the detection limit for DA was very low (down to nM). This is because DA can remarkably enhance the luminescence intensity of the Tb(3+) ion by Y(3+) in the colloidal solution of AgNPs, forming a new co-luminescence system. Furthermore, based on the metal enhanced fluorescence (MEF), AgNPs can sensitize the co-luminescence effect of the complex of Tb(3+)-Y(3+)-DA. In a neutral buffer solution (pH 7.50), the luminescence intensity of the system was linearly related to the concentration of DA in the range of 2.0-100 nM, with a limit of detection as low as 0.57 nM. The proposed method was applied for the determination of DA in dopamine hydrochloride injections and human serum samples with good accuracy and satisfactory recovery.

Tremella-like graphene–Au composites used for amperometric determination of dopamine

Tremella-like graphene–Au composites were synthesized by a one-step hydrothermal method for selective detection of DA.

Electrochemical sensing using boronic acids

Boronic acids can bind with 1,2- or 1,3-diols to form five or six-membered cyclic complexes and also can interact with Lewis bases to generate boronate anions, making them suitable for the electrochemical sensing of these species

Fast, sensitive and selective colorimetric gold bioassay for dopamine detection

A highly sensitive and selective colorimetric biosensor for dopamine has been developed by using double molecular recognition modified Au nanoparticles.

Nanomaterials-based optical techniques for the detection of acetylcholinesterase and pesticides

The large amount of pesticide residues in the environment is a threat to global health by inhibition of acetylcholinesterase (AChE). Biosensors for inhibition of AChE have been thus developed for the detection of pesticides. In line with the rapid development of nanotechnology, nanomaterials have attracted great attention and have been intensively studied in biological analysis due to their unique chemical, physical and size properties. The aim of this review is to provide insight into nanomaterial-based optical techniques for the determination of AChE and pesticides, including colorimetric and fluorescent assays and surface plasmon resonance.

mga genosensor for early detection of human rheumatic heart disease

The 5' amino-labeled DNA probe complementary to mga gene of Streptococcus pyogenes was immobilized on carboxylated multiwall carbon nanotubes electrode and hybridized with 0.1-100 ng/6 μl single-stranded genomic DNA (ssG-DNA) of S. pyogenes from throat swab of suspected rheumatic heart disease (RHD) patients. Electrochemical response was measured by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance (EI). The sensitivity of the sensor was 106.03 (μA/cm(2))/ng and limit of detection (LOD) was found 0.014 ng/6 μl with regression coefficient (R(2)) of 0.921 using DPV. The genosensor was characterized by FTIR and SEM, and electrode was found stable for 6 months on storage at 4 °C with 5-6 % loss in initial DPV current. mga genosensor is the first report on RHD sensor which can save life of several suspected patients by early diagnosis in 30 min.

Carbon dots and chitosan composite film based biosensor for the sensitive and selective determination of dopamine

A simple, sensitive and reliable dopamine (DA) biosensor was developed based on a carbon dots (CDs) and chitosan (CS) composite film modified glassy carbon electrode (CDs-CS/GCE). Under optimal conditions, the CDs-CS/GCE showed a better electrochemical response for the detection of DA than that of the glassy carbon electrode (GCE). The oxidation peak current (Ipa) of DA was linear with the concentration of DA in the range from 0.1 μM to 30.0 μM with the limit of detection as 11.2 nM (3S/N). The CDs-CS/GCE was applied to the detection of DA content in an injection solution of DA with satisfactory results.

Electrochemical detection of β-amyloid peptides on electrode covered with N-terminus-specific antibody based on electrocatalytic O2 reduction by Aβ(1-16)-heme-modified gold nanoparticles

β-Amyloid (Aβ) peptides are believed to be important for the diagnosis and prognosis of Alzheimer's disease (AD) serving as reliable molecular biomarkers. In this work, we reported a simple and sensitive electrochemical strategy for the detection of total Aβ peptides using gold nanoparticles modified with Aβ(1-16)-heme (denoted as Aβ(1-16)-heme-AuNPs). Monoclonal antibody (mAb) specific to the common N-terminus of Aβ was immobilized onto gold electrode for the capture of Aβ(1-16)-heme-AuNPs. The anchored Aβ(1-16)-heme-AuNPs showed strong electrocatalytic O2 reduction. Pre-incubation of the mAb-covered electrode with native Aβ decreased the amount of Aβ(1-16)-heme-AuNPs immobilized onto the electrode, resulting in the decrease of the reduction current of O2 to H2O2. The competitive assay is sensitive and selective to Aβ peptides. The voltammetric responses were found to be proportional to the concentrations of Aβ ranging from 0.02 to 1.50nM, and a detection limit of 10 pM was achieved. To demonstrate the viability of the method for the analysis of Aβ in real sample, artificial cerebrospinal fluid (aCSF) containing Aβ(1-40), Aβ(1-42) and Aβ(1-16) was tested. We believe that the method would offer a useful means for quantifying Aβ in a biological matrix, and be valuable in the design of new types of electrochemical biosensors for the detection of peptides and proteins.

Luminescent ZnO quantum dots for sensitive and selective detection of dopamine

Water-soluble and luminescent ZnO quantum dots (QDs) capped by (3-aminopropyl) triethoxysilane (APTES) are environment-friendly with strong photoluminescence (max. wavelength: 530 nm). Interestingly, it was found that the fluorescence could be quenched by dopamine (DA) directly. On the basis of above, a novel ZnO QDs based fluorescent probe has been successfully designed to detect DA with high selectivity and sensitivity. Moreover, the possible fluorescence quenching mechanism was proposed, which showed that the quenching effect may be caused by the electron transfer from ZnO QDs to oxidized dopamine-quinone. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of DA within the range from 0.05 to 10 μM, with the detection limit down to 12 nM (n=3). Also, the selectivity experiment indicated the probe had a high selectivity for DA over a number of possible interfering species. Finally, this method was successfully used to detect DA in serum samples with quantitative recoveries (99-110%). With excellent selectivity and high sensitivity, it is believed that the ZnO QDs based fluorescent probe has a potential for the practical application in clinical analysis.

Sandwich-type electrochemical biosensor for glycoproteins detection based on dual-amplification of boronic acid-gold nanoparticles and dopamine-gold nanoparticles

Glycoproteins play important roles in a wide variety of biological processes. The change in the concentration levels has been associated with many cancers, as well as other diseases. Thus, rapid, sensitive and selective determination of glycoproteins is much preferred. In this work, we reported a sandwich-type electrochemical biosensor based on dual-amplification of 4-mercaptophenylboronic acid (MBA)-capped gold nanoparticles (MBA-AuNPs) and dopamine (DA)-capped AuNPs (DA-AuNPs). Biological recognition elements such as synthetic receptor and aptamer immobilized onto gold electrodes were used to capture glycoproteins. The captured glycoproteins were then derivatized with MBA-AuNPs through the formation of tight covalent bonds between the boronic acids of MBA-AuNPs and diols of glycoproteins. Electroactive DA-AuNPs were attached by the anchored MBA-AuNPs via the interaction of boronic acids with DA tags, which facilities the amplified voltammetric detection of glycoproteins. With avidin and prostate specific antigen (PSA) as model analytes, we demonstrated the feasibility and sensitivity of the proposed method. The results indicated that sub-picomolar avidin/PSA can be readily measured. We believe that this strategy will be valuable for the electrochemical detection of other glycoproteins.

Simple, fast and selective detection of adenosine triphosphate at physiological pH using unmodified gold nanoparticles as colorimetric probes and metal ions as cross-linkers

We report a simple, fast and selective colorimetric assay of adenosine triphosphate (ATP) using unmodified gold nanoparticles (AuNPs) as probes and metal ions as cross-linkers. ATP can be assembled onto the surface of AuNPs through interaction between the electron-rich nitrogen atoms and the electron-deficient surface of AuNPs. Accordingly, Cu2+ ions induce a change in the color and UV/Vis absorbance of AuNPs by coordinating to the triphosphate groups and a ring nitrogen of ATP. A detection limit of 50 nM was achieved, which is comparable to or lower than that achievable by the currently used electrochemical, spectroscopic or chromatographic methods. The theoretical simplicity and high selectivity reported herein demonstrated that AuNPs-based colorimetric assay could be applied in a wide variety of fields by rationally designing the surface chemistry of AuNPs. In addition, our results indicate that ATP-modified AuNPs are less stable in Cu2+, Cd2+ or Zn2+-containing solutions due to the formation of the corresponding dimeric metal-ATP complexes.