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A solvent-assisted ESIPT fluorescent dye was synthesized and used as a probe (2-PPN) for the detection of F−/Ag+ and high-resolution imaging of the cilia in live cells. The developed ESIPT fluorophore exhibited strong tautomeric fluorescence in protic solvents and normal emission in aprotic solvents, which is a significant departure from that of conventional intramolecular ESIPT compounds. The H-binding interaction of F− and the chelation of Ag+ with the ESIPT module of 2-PPN resulted in significant tautomeric emission quenching. From this basis, the 2-PPN-based assays for the detection of F− and Ag+ were established. The detection limit for F− and Ag+ sensing is 2.4 nM and 1.5 nM, respectively. The selective experimental results showed that no tautomeric fluorescence change of 2-PPN could be observed in the presence of the other inorganic ions in the same medium, revealing high selectivity of 2-PPN to F− and Ag+. Furthermore, MTT assay experiments proved that the probe 2-PPN exhibited low cytotoxicity and good cell membrane permeability. The probe was also further successfully utilized to image the cilia in vitro MCF7 cells, displaying its high-resolution imaging performance. Graphical abstract

Excited-state intramolecular proton transfer (ESIPT)-exhibiting polymer nanoparticles (e-PNPs) were prepared using 2,6-diformyl-4-methylphenol and guanidine hydrochloride. The e-PNPs bear abundant aromatic o-OH, CN and NH2 groups which are responsible for ESIPT modules. By incorporating ESIPT units into nanostructures, the ESIPT moieties can achieve an appropriate hydrophobic environment for the ESIPT reaction, enabling e-PNPs to show strong ESIPT-fluorescence. Upon the addition of Cu(II), the tautomeric fluorescence (t-FL) of e-PNPs is significantly quenched because of the coordination of Cu(II) with e-PNPs. The presence of cysteine (Cys) can elicit the t-FL recovery of e-PNPs–Cu(II) complexes due to the chelation interaction between Cu2+ and the sulfhydryl and amino groups of Cys. Based on this signalling mechanism, the e-PNPs–Cu(II) sensing system was used to detect Cys, and the linear range and limit of detection of the nanosensing system were 0–6.3 μM and 1.8 nM, respectively. As expected, this method was successfully applied to the determination of Cys in rabbit serum and plasma samples with satisfactory recovery ranging from 97.4 to 105.6%. Moreover, e-PNPs–Cu(II) based nanoprobes were employed for imaging Cys in live cells, which demonstrated their potential values for bioanalytical applications.

Artemisinin (ART) and its derivatives are first-line treatment drugs for falciparum malaria and save millions of lives every year. It is very difficult to design specific fluorescent probes for ART because ART has no groups for binding to except for the peroxide group. We find that alkaline-hydrolyzed ART (a-ART) can specifically recognize and react with vitamin B1 (VB1) and produce fluorimetrically detectable thiochromes. Notably, this chemistry is affected by very low concentrations of a-ART in a Tris–HCl buffer solution (pH 7.5) at room temperature, leading to >260-fold enhancement in the blue emission at 442 nm. By making use of the new signaling mechanism, an effective strategy for detecting ART was developed. The fluorescence intensity of the VB1-based probes linearly increased with increasing ART concentration ranging from 1 to 230 μM mL−1, and a detection limit as low as 11.5 nM mL−1 was achieved, making this method more sensitive than other reported UV-vis absorption and electrochemical methods. Moreover, this assay shows good selectivity over other ions and biomolecules. The proposed method was applied for the determination of ART in tablets and dried leaf samples of Artemisia annua L. with satisfactory results, which confirms its great potential for real sample analysis. The designed assay avoids the preparation of fluorescent probes, and all the detection processes are accomplished within 20 min. Therefore, VB1 can offer a simple, highly sensitive and selective sensing model for fluorescence detection of ART.

Intrinsically fluorescent polymer nanoparticles (F-PNPs) were synthetized from 2-hydroxy-5-methylisophthalaldehyde and melamine by solvothermal method. F-PNPs can emit strong yellow green fluorescence at 542 nm without the conjugation to any external fluorescent agent and surface modification. Owing to the abundant amino and hydroxyl groups on their surface, the F-PNPs possess multiple binding sites, good biocompatibility and excellent water-solubility. Addition of Zn2+ to the F-PNPs solution resulted in a blue shift (Δλ=40 nm) with obvious enhancement in the fluorescence intensity at 502 nm; while there was negligible change in the presence of other metal ions. The subsequent treatment with pyrophosphate (PPi) can cause fluorescence recovery of F-PNPs by pulling the Zn2+ out of the coordination cavity of F-PNPs-Zn2+ nanocomposites. No interference was observed from other anions and nucleotides, making the F-PNPs-Zn2+ ensembles highly sensitive and selective nanoprobes for PPi. The detection limit is 2.75 × 10−8 M/L and 7.63 × 10−8 M/L for Zn2+ and PPi, respectively. The proposed nanoprobes were then used for detecting the recovery of Zn2+ and PPi in rabbit serum samples, which were found to be 99.4–104.2% and 98.6–104.7%, respectively. The present strategy for the fabrication of nanoparticles may offer a new sight for the preparation of polymer nanostructures. The F-FNPs based probes can provide an accurate method for the detection of Zn2+ and PPi in serum samples.

A facile approach was developed to prepare fluorescent nitrogen-rich quantum dots (NCQDs) using 2-azidoimidazole and ammonium hydroxide as reactants. The nitrogen and carbon elements of NCQDs form the frameworks of their nanostructures together and bear multiple active sites. By using NCQDs as fluorophores and graphene oxide (GO) as controllers, a hydrogen binding-based nanosensor was constructed for the detection of pyrophosphate (PPi). In NCQDs-GO sensing assemblies, the binding of GO to NCQDs results in the fluorescence quenching by FRET mechanism; while the addition of PPi leads to the fluorescence recovery of NCQDs because of the competitive binding between NCQDs and PPi to GO. The fluorescence intensity showed linearity with the added PPi concentration ranging from 0 to 400 μM with the detection limit of 8.3 nM (σ = 3). This procedure for the fabrication of amino-functionalized carbon quantum dots is simpler and more efficient compared to conventional doping and surface modification methods. The proposed NCQDs-GO sensing assemblies showed high selectivity and sensitivity to PPi over the competing anions in aqueous solution.

Strongly green fluorescent carbon dots (CQDs) have been directly synthesized from 2,4-diaminophenylhydrazine and 2-hydroxy-5-methylisophthalaldehyde through a facile solvothermal method. The novel CQDs exhibit high fluorescence quantum yield and excellent water solubility due to the abundant amino and hydroxy groups on their surface. The use of the as-prepared CQDs combined with Cu2+ constructed a “turn-on” switch cysteine-responsive nanoprobe. In the CQDs-Cu2+ assemblies, the binding of Cu2+ to CQDs results in the fluorescence quenching of CQDs by electron transfer mechanism, while the addition of cysteine leads to the fluorescence recovery because of the competitive binding between cysteine and CQDs to Cu2+. The nanoprobes showed high sensitivity to cysteine with the detection limit of 2.6 nmol L−1. The selectivity investigation results demonstrated that the Cu2+-integrated nanoparticles were highly selective toward cysteine over the other amino acids and biologically related metal ions. The proposed nanoprobe was then employed for detecting the recovery of cysteine in rabbit serum and plasma samples and imaging the cysteine in cancer cells, and the recovery was found to be 98.2–104.0%. This “synthesis-modification integration” strategy for the fabrication of CQDs may offer a new sight for the preparation of multifunctional nanostructures and broadening the application of CQDs in bioimaging.

As a new member of the carbon quantum-dot family, fluorescent nitrogen-rich quantum dots (NRQDs) were prepared by a mixed solvothermal method using 2-azidoimidazole and aqueous ammonia as reactants. These NRQDs are rich in nitrogen up to 40.2%, which are endowed with high fluorescence quantum yield, good photostability, water-solubility and favourable biocompatibility. We further explored the use of NRQDs combined with Cu2+ as a nanoprobe for sensing fluorescently of cysteine (Cys) in complex biological samples. In this sensing system, the fluorescence is significantly quenched via energy transfer from NRQDs to Cu2+ for the coordination of amino-containing groups with Cu2+. The strong affinity between Cu 2+ and Cys leads to the formation of Cu2+-Cys complexes and cause the detachment of Cu2+ from the surface of NRQDs, thus the fluorescence of NRQDs recover. This nanoprobe allows analysis of Cys by modulating the switch of the fluorescence of NRQDs with a detection limit of 5.3nM. As expected, the proposed NRQDs-Cu2+complex-based nanoprobes were successfully applied for the determination of Cys in human serum and plasma samples with recoveries ranging from 97.2% to 105.7%. The probe ensemble was also successfully applied to imaging of Cys in living cells with satisfactory results, which shows strong potential for clinical diagnosis.

An efficient signal enhancement strategy for the detection of cysteine (Cys) was developed, which is based on the combination of a Cys-reduced reaction and the chelation of Al3+ with the Cys-promoted product. The Cys probe S-DPM was prepared by adding a 2,4-dinitrobenzenesulfonyl group onto a 2′-hydroxyldihydropyrimidobenzimidazole derivative (DPM). Upon treatment with Cys, S-DPM was reduced and the hydroxyl group was released in the product DPM, thereby enabling an excited-state intramolecular proton transfer (ESIPT) process. When Al3+ ions were added, the fluorescence signal was dramatically increased owing to the transformation of the DPM into DPM-Al3+ complexes with a very high fluorescence quantum yield (0.865). The proposed method allows the analysis of Cys by modulating the switch of the fluorescence of S-DPM with Cys ranging from 0.01 to 4.5 μM. The detection limit is 17 nM. As expected, the S-DPM probe was successfully applied for the determination of Cys in human serum and plasma samples with recoveries ranging from 97.2.0% to 105.5%. Fluorescence imaging experiments showed that S-DPM can track Cys in living cells. ESIPT compounds are frequently used for the construction of Cys probes, but this method measures the fluorescence of only a part of the Cys-reduced products. The use of S-DPM coupled with Al3+ overcomes this drawback.

One-pot reaction approach to the synthesis of dihydropyrimido-diindole fluorophores (DPDI) was developed. In DPDI molecules, the two pyrrole rings in dipyrromethane were bridged by a carbon atom, eliciting a six-membered ring and rigid planar structure. Photophysical measurements demonstrated that DPDI can exhibit strong fluorescence, large Stokes shift and low sensitivity to pH. Cyclic voltamogram indicated a pair of redox peaks of DPDI near ±0.48V, implying that DPDI can be oxidized by nitrite (NO2−). In the presence of NO2−, DPDI showed apparent change in colours and fluorescence intensity owing to the implantation of NO2−. From this basis, a highly sensitive and selective analysis of NO2− was established using DPDI as probes, which offered a sensitive determination of NO2− in the concentration range of 0–17 μM with the detection limit of 2.2 nM. Furthermore, DPDI was employed for fluorescence imaging, demonstrating the ability to discriminate from different concentrations of NO2− in living cells. The newly developed DPDI dyes showed the obvious advantages of facile preparation and large Stokes shift over conventional dipyrrole-based phosphors.

The nano biosensors based on gold cap-shaped nano-particles like polystyrene and silica nanospheres have been successfully prepared on the substrates of disposable plate (96 wells) and miniplate (72 wells). The sensing film of carboxymethyl dextran layer was modified on the gold surface of the cap-shaped nano-particles. The corresponding micro-device with four channel of optical sensing system has been well constructed and applied to detection of anti-avidin D protein and biotinylated DNA molecules. The DNA hybridization reaction has also been real-time and parallel monitored in four channels, showing that the device possessed a nice reproducibility, which opens a promising bioanalytical application in practice.

The gold colloidal nanoparticles with a diameter of 24 ± 0.2 nm were prepared, characterized by ultraviolet–visible (UV-vis), transmission electron microscopy (TEM), and cyclic voltammetry, and assembled on a gold plate substrate for constructing an optical nanobiosensor. The nanosensor exhibited distinct optical properties of localized surface plasmon resonance (LSPR), which could be used for recognition of oncogene biomolecules such as the c-Myc (3C7) antibody protein. The LSPR nanobiosensor has also been successfully applied to determination of a pCMV-Myc mammalian expression vector, one kind of DNA plasmids with a linear response range of 6.2–20.0 ng/µL and a detection limit of 2.4 ng/µL.

A cyanidin-based horseradish peroxidase (HRP)-catalyzed reaction system was established in this work. In B-R buffer solutions (pH 6.8), a UV-visible absorbance peak of cyanidin (CAG) at 540 nm (A p1) appeared. After the oxidation reaction of CAG catalyzed by HRP in the presence of H2O2, a significant absorbance peak at 482 nm (A p2) occurred. The ratio R(A P2/A P1) was proportional to the HRP concentration. The application of CAG in the enzyme-linked immunosensing assays was investigated using food and mouth disease virus antigen (FMDVAg) as a model analyte. In sandwich immunoreaction, the analyte FMDVAg and food and mouth disease virus antibody (FMDVAb)-modified magnetic nanoparticles bound the supported conconvalina (Con A) bound with HRP-FMDVAb. After de-absorbing and separating, the HRP-FMDVAb-FMDVAg-FMDVAb-magnetic nanoparticles complexes were subject to enzymatic reaction and UV-visible absorbance measurements. The HRP moiety of the immunoreaction complexes can catalyze the oxidation reaction of CAG by H2O2, and the substrate CAG is converted to products. Based on this principle, a sandwich assay model has been employed to determine FMDVAg in rabbit serum samples with the aid of FMDVAb-Fe3O4 magnetic nanoparticles. The linear range of the FMDVAg determination is 1.5×10−8−2.7×10−6 g/mL with the relatively standard deviation of 3.7% (n = 11). The detection limit is 3.1×10−9 g/mL. Additional advantages of the typical substrate such as OPD, OAP and TMB are good water-solubility and stability.

A novel technique of immobilizing indicator dyes by electrostatic adsorption and covalent bonding to fabricate optical sensors was developed. 3-Amino-9-ethylcarbazole (AEC) was attached to the outmost surface of quartz glass slide via aminosilanizing the slide, crosslinking chitosan, adsorbing Au nanoparticle, self-assembling HS(CH2)11OH, and coupling AEC. Thus, an AEC-immobilized optical sensor was obtained. The sensor exhibits a wide linear response range from 7.0×10−7 to 1.0×10−4 mol/L and a correlation coefficient of 0.995 9 for the detection of 2-nitrophenol. The detection limit and response time of the sensor are 1.0×10−7 mol/L and less than 10 s, respectively. The fluorescence intensity of the used sensor can be restored to the blank value by simply rinsing with blank buffer. A very effective matrix for immobilizing indicator dye is provided by the proposed technique, which is adaptable to other indicator dyes with amino groups besides AEC.

We have monitored a gold corrosive dissolution behavior accompanied in n -alkanethiol like n -dodecanethiol assembled process with in situ quartz crystal microbalance (QCM), and then observed it with atomic force microscopy (AFM) which showed an evident image of corrosive defects or holes produced on gold substrate, corresponding to gold dissolution induced by the alkanethiol molecules in the presence of oxygen. For detection of the dissolved gold defects during alkanethiol assembled process, an atomic absorption spectroscopy (AAS) has been carried out in this paper, and the detection limit for the dissolved gold could be evaluated to be 15.4 ng/mL. The amount of dissolved gold from the substrates of gold plates as functions of immersion time, acid media, solvents and thiol concentration has been examined in the oxygen saturated solutions. In comparison with in situ QCM method, the kinetics behavior of the long-term gold corrosion on the gold plates in 1.0 mmol/L of n -dodecanethiol solution determined with AAS method was a slow process, and its corrosion rate on gold dissolution could be evaluated to be about 4.4 × 10 − 5 ng·cm − 2 ·s − 1 , corresponding to 1.3 × 10 8 Au atoms·cm − 2 ·s − 1 , that was much smaller than that of initial rate monitored with in situ QCM. Both kinetics equations obtained with QCM and AAS showed a consistent corrosion behavior on gold surfaces.

A novel technique of covalent immobilization of indicator dyes in the preparation of fluorescence sensors is developed. Silver nanoparticles are used as bridges and carriers for anchoring indicator dyes. 3-amino-9-ethylcarbazole (AEC) was employed as an example of indicator dyes with terminal amino groups and covalently immobilized onto the outmost surface of a quartz glass slide. First, the glass slide was functionalized by (3-mercaptopropyl) trimethoxysilane (MPS) to form a thiol-terminated self-assembled monolayer, where silver nanoparticles were strongly bound to the surface through covalent bonding. Then, 16-mercaptohexadecanoic acid (MHDA) was self-assembled to bring carboxylic groups onto the surface of silver nanoparticles. A further activation by using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) converted the carboxylic groups into succinimide esters. Finally, the active succinimide esters on the surface of silver nanoparticles were reacted with AEC. Thus, AEC was covalently bound to the glass slide and an AEC-immobilized sensor was obtained. The sensor exhibited very satisfactory reproducibility and reversibility, rapid response and no dye-leaching. Rutin can quench the fluorescence intensity of the sensor and be measured by using the sensor. The linear response of the sensor to rutin covers the range from 2.0 x 10(-6) to 1.5 x 10(-4) molL(-1) with a detection limit of 8.0 x 10(-7) molL(-1). The proposed technique may be feasible to the covalent immobilization of other dyes with primary amino groups.

A natural product, stilbene glycoside (2,3,5,4'-tet rahydroxy- diphenylethylene-2-O-glucoside, TBG), has been evaluated for the first time as a potential substrate for horseradish peroxidase (HRP )-catalyzed fluorogenic reactions. The properties of TBG as a fluorogenic substrate fo r HRP and its application in a fluorometric enzyme-linked immunosensing system were compared with commercially available substrates such as p-hydroxyphenylpropionic acid (pHPPA), chavicol and Amplex red using Brucella melitensis antibody (BrAb) as a model analyte. The immunosensing body based on HRP-BrAb was constructed by dispersing graphite, BrAg and paraffin wax at room temperature. In a competitive immunoassay procedure, the BrAb competed with HRP-BrAb to react with the immobilized BrAg. In the enzymatic reaction, the binding HRP-BrAb on the sensing body surface can catalyze the polymerization reaction of TBG by H 2O2 forming fluorescent dimers and causing an increase in fluorescence intensity. TBG showed comparable ability for HRP detection and its enzyme-linked immunosensing reaction system, in a linear detection ranging of 3.5 ×10 -8 ~7.6 ×10 -6 g/L and with a detection limit of 1.7 ×10 -9 g/L. The immobilized biocomposite surface could be regenerated with excellent reproducibility (RSD=3.8%) by simply polishing with an alumina paper. The proposed immunosensing system has been used to determine the BrAb in rabbit serum samples with satisfactory results.

An amperometric artemisinin (ARN) sensor based on the supramolecular recognition of glycosylated metalloporphyrin, which is included in the Au-nanoparticles-chitosan film coated on the glass carbon electrodes, was developed. For the improvement of the selectivity of artemisinin detection, 5,10,15,20-tetrakis[2-(2,3,4,6-tetraacetyl-β- d -glucopyranosyl)-1-O-phenyl]porphyrin (T(o-glu)PPH) metal complex [FeT(o-glu)PPCl] was synthesized and employed as a ARN-sensitive and -selective material in the amperometric sensors. The proposed [FeT(o-glu)PPCl]/Au-nanoparticles modified electrodes showed excellent selectivity and sensitivity toward ARN with respect to a number of interferents and exhibited stable current response, which can be attributed to the coordination of ARN with the [FeT(o-glu)PPCl] in the electrodes. The calibration graph obtained with the proposed sensor was linear over the range of 1.8 × 10−7–1.7 × 10−9 mol l−1, with a detection limit of 1.7 × 10−9 mol l−1 for ARN. Significant advantages of the proposed procedure over the conventional reductive electrochemical methods are the selective detection and the relatively low applied potential requirement of the ARN-sensor. The prepared sensor is applied for the determination of ARN in plant samples and the results agreed with the values obtained by the pharmacopoeia method.

The frequency response characteristics for twenty-two organic vapours by piezoelectric thickness-shear-mode (TSM) acoustic wave sensors coated with four supramolecule compounds—calixarenes have been investigated. Among them, 2,8,14,20-tetraethyl-4,6,10,12,16,18,22,24-octahydroxylcalix[4]arene (I) was the most efficient actively adsorptive material for host–guest recognizing alkyl ketone molecules such as 2-butanone and acetone. The supramolecule recognition mechanism has been discussed, that is based on the formation of C–H⋯π bond interaction between the methyl group of ketone molecule and the phenyl ring of the calixarene compound. The linear range of the TSM sensor upon exposure to 2-butanone vapour was 0–940.5 ppm with a detection limit of 2.67 ppm when the coating mass of the compound I was selected as 19 μg. The kinetics behaviours in the adsorption and desorption processes have been examined with polynomial curve fitting procedure. Furthermore, the proposed TSM sensor possessed good selectivity, reversibility, reproducibility and high stability. Compared with gas chromatography (GC) method, the proposed sensor can be used for on-line determination of 2-butanone vapour in air with a recovery of 94.8–106.5%, which was in consistent with those obtained by GC method.

The self-assembled monolayers (SAMs) of alkanethiols such as 1-dodecanethiol (DDT) on the surface of polycrystalline gold grain on quartz crystal microbalance (QCM) at room temperature and alkynethiols such as phenylethynyl thiol (PET) on the surface of Au(111)/mica under − 65 °C have been fabricated. A multimode scanning probe microscope (SPM) investigation for the first time reveals the formation of stripe domain of DDT SAMs together with roundish domain. This feature was not caused by an annealing treatment but might be induced by coexistence of a few different facets and reconstruction of the surface on the grain. The stripe domain of PET SAMs could also be found on the surface of the grain, which was within the substrate of the gold/mica. It shows that the feature of the stripe domain for organothiol monolayers self-assembled on gold grain surfaces possesses a certain generality. Furthermore, the arrangement of organothiol stripe domain can be well understood from the interpretation of the relationship between the stripe width and width direction, molecule interval distance, molecule length and tilt angles of the thiols.

An amperometric dimetridazole (DNZ) sensor based on the supermolecular recognition by glycosylated metalloporphyrin, which was immobilized on a glassy carbon electrode by chitosan, is reported. For the preparation of a DNZ-sensitive active material, 5,10,15,20-tetrakis[2-(2,3,4,6-tetraacetyl-β- d -glucopyranosyl)-1- O -phenyl]porphyrin (T( o -glu)PPH 2 ) and its Mn(III) complex MnT( o -glu)PPCl were synthesized from the reaction of pyrrole with ortho -acetylglycosylated benzaldehyde by Lindsay's method. The MnT( o -glu)PPCl-modified electrode showed excellent selectivity toward DNZ with respect to a number of interferents and exhibited stable response. The calibration graph obtained with the proposed sensor was linear over the range of 1.5 × 10 −3 to 2.7 × 10 −9 M/L, with a detection limit of 2.7 × 10 −9 M/L for DNZ. Cyclic voltammetric measurements indicated that MnT( o -glu)PPCl entrapped in chitosan matrices could decrease the reduction potential for DNZ detection. The sensor could be regenerated by washing in an alcohol solution, with an excellent reproducibility (R.S.D. = 2.6%). The experimental conditions such as pH and applied working potential were optimized. The prepared sensor is applied for the determination of DNZ in pharmaceutical preparations and the results agreed with the values obtained by the pharmacopoeia method.

The adsorption response behaviors with n‐alkanethiol self‐assembled monolayers (SAMs) formed on the surface of polycrystalline gold grains have been investigated in nitrogen and oxygen saturated tetrahydrofuran (THF) solutions by using in situ quartz crystal microbalance (QCM) and atomic force microscopy (AFM). Comparing with frequency‐decreased process in the nitrogen saturated solution, the response behavior shows a frequency increased process in the oxygen saturated solution, indicating that the gold corrosion is accompanied to occur in the self‐assembled process of organothiol that is due to the thiol induction and oxygen oxidation. In the presence of thiol and oxygen, the corrosion effect is stronger than the adsorption effect of organothiols, such as n‐dodecanethiol molecules on gold, which causes gold loss from the QCM surface, made evident from the observation of many corrosive defects or holes produced on the surface of gold grains by AFM image. Furthermore, the kinetic behavior on the c...

A capacitive chemical sensor for fenvalerate is reported. By using ac impedance measurements the sensor has been based on the decrease in capacitance caused by the analyte used as the template in the formulation of an electropolymerized molecularly imprinted polymer as receptor layer. Improvement of the insulating properties of the sensor was investigated in detail. The capacitive sensor was prepared by a deposition of a self-assembled monolayer of 2-mercaptobenzimidazole (2-MBI) before electropolymerization of 2-MBI and subsequent treatment with n-dodecanethiol to eliminate pinholes and defects in the polymerized 2-MBI film. From the calibration curve concentrations of fenvalerate up to 9 microg mL(-1) could be detected with a linear determination range up to 5 microg mL(-1) and a detection limit of 0.36 microg mL(-1). No significant interference was observed from common pyrethroid insecticides.

A renewable fluorometric enzyme immunosensing system using prochlorperazine (PCP) as the substrate for horseradish peroxidase (HRP) has been developed for the determination of transferrin in serum samples. This system is based on paraffin–graphite–transferrin antibody immunocomposite, which permits its surface to be easily regenerated by simply polishing. The renewed surface served as a platform for the competitive immunoreaction of HRP–transferrin and free transferrin (analyte) with the immobilized antibody bound to the surface and for HRP-catalyzed reaction. By using prochlorperazine as the substrate for HRP, the amount of HRP–transferrin bound was quantified fluorimetrically, which was in turn related to free transferrin content in the samples. Prochlorperazine as the substrate, possesses a satisfactory activity towards HRP as compared to p -hydroxyphenylacetic acid. The analytical conditions, such as pH, the amount of labeled transferrin, incubation time, and temperature were studied in detail. Under the optimized experimental conditions, a detection limit of 7.3 ng/ml and the linear detection ranging from 7.3 to 127 ng/ml were obtained. This approach has been applied to clinical samples with satisfactory results.

A new strategy to construct amperometric immunosensor for Schistosoma japonicum antigen (SjAg) assay based on nano-size particulate gold (nano-Au) monolayer as sensing platform has been described. The nano-Au monolayer was obtained through chitosan-entrapped carbon paste electrode (CCPE). The high affinity of chitosan entrapped in CCPE for nano-Au associated with its amino groups facilitated the formation of nano-Au monolayer on the surface of CCPE. A sequential competitive immunoassay format was performed on the nano-Au monolayer supported by CCPE using S. japonicum antibody (SjAb) and SjAg as a model system. The assay comprised first loading of SjAb on nano-Au monolayer, then blocking in BSA solution, followed by a competitive incubation in the buffer containing the SjAg (analyte) and SjAg labeled with horseradish peroxidase (HRP) and finally the amperometric detection with hydroquinone as an enzymatic substrate. The dynamic concentration range for SjAg assay is 0.11–22.4 μg ml −1 with a detection limit of 0.06 μg ml −1 . The feasibility of regenerating nano-Au monolayer for consecutive assays was demonstrated by a simple chemical treatment after each determination. The simple manipulations of construction of nano-Au monolayer, low-cost and improved sensitivity are main features of proposed immunosensing method.

An amperometric metronidazole (MTZ) sensor using a glycosylated metalloporphyrin as a recognition element, which was incorporated in a carbon paste electrode, is reported. For the preparation of a MTZ-sensitive active material, 5, 10, 15, 20-tetrakis [2-(2, 3, 4, 6-tetraacetyl-β-D-glucopyranosyl)-1-O-phenyl]porphyrin (T(oglu) PPH2) and its Mn(III) complex MnT(o-glu)PPCl were synthesized from the reaction of pyrrole with ortho-acetylglycosylated benzaldehyde by Lindsay’s method. The MnT(oglu) PPCl-modified electrode showed excellent selectivity toward MTZ with respect to a number of interferents and exhibited stable response. The calibration graph obtained with the proposed sensor was linear over the range of 2.9×10-3-5.8×10-8 M/L, with a detection limit of 5.8×10-8 M/L for MTZ. Cyclic voltammetric measurements indicated that MnT(oglu) PPCl included in graphite-epoxy resin matrices could efficiently mediate electron transfer from the base electrode to MTZ causing a decrease of reduction potential for MTZ detection. The sensor could be regenerated by simply polishing with an alumina paper, with an excellent reproducibility (RSD=1.6%). The experimental conditions such as pH and applied working potential were optimized. The prepared sensor is applied for the determination of MTZ in pharmaceutical preparations and the results agreed with the values obtained by the pharmacopoeia method.

A fluoroimmunosensing system with the use of ferulic acid as the substrate for the determination of transferrin in serum samples has been developed. It was based on paraffin–graphite–transferrin antiserum immunocomposite, which permits its surface to be easily renewed by polishing. The renewed surface serves as a platform for the competitive immunoreaction of HRP-transferrin and free transferrin (analyte) with the antibody bound to the surface. By using ferulic acid as a substrate, the amount of HRP-transferrin bound was quantified fluorimetrically, which was in turn related to free transferrin content in the samples. Ferulic acid as the substrate possesses a better stability towards H2O2 as compared to TMB. The analytical conditions, such as pH, the amount of labeled transferrin, incubation time, and temperature were studied. Under the optimized experimental conditions, a detection limit was 30 ng/mL and the linear detection range was from 39.3 to 177 ng/mL. This approach has been applied to cli...

An amperometric immunosensor system for assay of an important poultry infectious disease Newcastle disease antibody (ND.Ab) has been developed. The Newcastle disease antigen (ND.Ag) was immobil- ized in a graphite paste matrix. The assay procedure is based on the bioreaction of the analyte ND.Ab and enzyme labeled HRP-ND.Ab competing for the ND.Ag sites at the newly regenerated biocomposite surface. The determination is accomplished by amperometry using tetramethylbenzidine and H2O2 as the substrates. Two different graphite pastes were compared using either sol–gel or solid paraffin as binders. The sol–gel biocomposite showed a better response characteristics and higher reproducibility. The ND.Ab can be determined up to 443.24 ng/mL with a detection limit of 11.1 ng/mL. The recovery studies in serum samples show the feasibility of practical application of the proposed method.

An immunosensing system for Brucella melitensis antibody (BrAb) assay which is useful for the diagnosis of brucellosis has been developed. To circumvent the difficulty of regeneration of immunocomposite surface, the natural material of microcellulose–paraffin was adopted, and it resulted in a considerable retention of the activity of the absorbed and encapsulated B. melitensis antigen (BrAg). The surface of the immunocomposite layer prepared was easily renewed by simple polishing. The renewed surface served as a platform for the competitive immuno-reaction of horseradish peroxidase (HRP)–BrAb and BrAb with BrAg bound to the surface. By using 3,3′,5,5′-tetramethylbenzidine (TMB) as the substrate, the amount of HRP–BrAb bound is quantified fluorimetrically, which is in turn related to the BrAb (analyte) content in samples. The amplification effect was obtained by using the enzymatic reaction, and an improved detection limit of 2.7 ng/ml was thus realized. The optimum analytical conditions such as pH, the amount of the labeled antibody and the flow rates of the substrate carrier solution were studied. The proposed method shows a pseudo linear response ranging from 2.7 to 90 ng/ml. The method has been employed to determine BrAb in serum samples.

A novel amperometric immunosensor setup is described which uses horseradish peroxidase (HRP) as a label in conjunction with a current-based Brucella sensor. The Bacteria modified immunosensor was constructed by using a bio-composite formed by dispersing graphite powder into a mixture of Brucella melitensis and silicate polymer gel. The enzyme-labeled antibody can readily diffuse toward the encapsulated antigen (Brucella melitensis), which retains its binding properties, and the association reaction is easily detected at the surface exposed to the solution. The use of an o-aminophenol (o-AP) substrate and amperometric detection at -150 mV (vs. SCE) results in a relatively low detection limit of 3.5 ng/ml and a linear detection range of 3.5 ng/ml to 200 ng/ml. Based on an optimized parameter, the prepared sensor was used to detect the Brucella melitensis antibody in serum samples by using a competitive binding assay. The results demonstrate the feasibility of employing the proposed immunosensor for the detection for Brucella melitensis antibody in a clinical analysis.

A multi-walled carbon nanotubes (MWNTs) film modified glassy carbon electrode (GCE) has been fabricated and showed potent electrocatalytic activity toward the electrochemical oxidation of salbutamol sulfate in phosphate buffer solution (pH=7.4). The linear dependence between the oxidation peak current of salbutamol sulfate and its concentration was observed in the range from 5.0 – 25 µmol/L with a detection limit of 1.0 µmol/L. The electrode possessed a nice recovery of 97.2 – 104.4% with good reproducibility and stability for detection of salbutamol sulfate aerosol samples, indicating that it was a feasible method for determination of salbutamol sulfate in actually pharmaceutical samples.

In this paper, the optical biosensors based on cap- shaped gold nano-particles have been constructed by evaporating gold on polystyrene and silica microspheres to form Au caps, which show a novel localized surface plasmon resonance (LSPR). The gold surface on silica spheres modified with a carboxymethyl dextran layer was used for sensing of anti-avidin D with a detection limit of 5.0 nmolldrL-1 and a sensitivity of 3.4 times 10-3 nmldrLldrnmol-1, which was based on surface-bound avidin molecule. Furthermore, a double stranded DNA (dsDNA) with a binding site of hexa sequence AGGTCA for a nuclear receptor, retinoid X receptor beta (RXRbeta), has been successfully immobilized on gold surface via a specific interaction between biotin moiety and streptavidin, and applied to selective recognition of small molecule nuclear ligands like 9-cis retinoic acid.

We have proposed an electrochemical detection method for DNA molecules based on an extended gate field effect transistor (EGFET) sensing chip which consists of one gold plate for molecule recognition and FET part for signal transduction. DNA Probes were immobilized on the gold plate by forming mixed monolayers of thiolated single-stranded oligonucleotide (HS-ssDNA) and alkanethiols, like 6-hydroxy-1-hexanethiol (6-HHT). Electrode reaction corresponding to the reductive desorption of the adsorbed monolayers in strong alkali solution was presented for quantification of surface density of DNA by using fast cyclic voltammetry (FCV). The passivation effects of surface modification with different functional groups on the potential behavior of the gold electrode were also examined. It was feasible to use EGFET chip for detection of DNA hybridization reaction, that the hybridization efficient was estimated to be about 40%.

An optical biosensor with surface bound gold cap-shaped nano particles like polystyrene nanospheres has been constructed for detection of bio-molecules like antigen, antibody protein and DNA plasmid, which exhibited distinct optical properties of localized surface plasmon resonance (LSPR). It caused 1.09 nm red shift in the peak wavelength (lambdamax) of LSPR spectrum for the nanosensor exposed to c-Myc (3C7) mouse monoclonal IgG and 3.53 nm red shift to the corresponding antibody by the immuno -reaction subsequently. The kinetic process for the activity of the c-Myc (3C7) antigen lost with the time has been examined. The LSPR nanobiosensor was also applied to recognition of a DNA plasmid of pCMV-Myc Mammalian Expression Vector, which would provide valuable information on molecular biology in clinical medicine, disease prediction, gene mutation and gene diagnosis.

The quantitative structure–activity relationship (QSAR) for neutral carriers used to prepare hydrogen ion sensors has been studied. A series of synthesized carrier compounds were taken as the training set. Five molecular structure parameters of the compounds were calculated by using CNDO/2 algorithm and used as feature variables in constructing QSAR model. The lower and upper limits of the linear pH response range were taken as the activity measure. The corresponding model equations were derived from the stepwise regression procedure. With the established QSAR model, a new pH carrier, (4-hydroxybenzyl) didodecylamine (XIII) was proposed and synthesized. The PVC membrane pH electrode based on carrier XIII with a wide pH linear response range of 2.0–12.5 was prepared. Having a theoretical Nernstian response slope of 57.2 ± 0.3 mV/pH (n = 5 at 25 °C) without a super-Nernstian phenomenon, the sensor had low resistance, short response time, high selectivity and good reproducibility. Moreover, the sensor was successfully applied to detecting the pH value of serum samples.

A fluorescence sensor based on the supermolecular recognition by glycosylated metalloporphyrin for levamisole (LEV) assay is reported. For the preparation of a LEV-sensitive active material, 5, 10, 15, 20-tetrakis[2-(2, 3, 4, 6-tetraacetyl-β-D-glucopyranosyl)-1-O-phenyl] porphyrin and its metal complexes were synthesized and used in an optode membrane prepared by including glycosylated metalloporphyrin in chitosan matrice. The immobilized glycosylated metalloporphyrin is shown to be weakly fluorescent as a result of the inhibiting of the electron tansfer by central metal. The fluorescence enhancement of the metalloporphyrin modified optode membrane by LEV is based on the complexation with the central metal moiety of metalloporphyrin and weakening the inhibiting of the electron tansfer for metalloporphyrin. The glycosylated metalloporphyrin/chitosan optode membrane showed excellent selectivity toward LEV with respect to a number of interferents and exhibited stable response. The calibration graph obtained with the proposed sensor was linear over the range of 1.3 x 10 -5 -3.5 x 10 -7 M L -1 , with a detection limit of 3.5 x 10 -7 M L -1 for LEV. The prepared sensor is applied for the determination of LEV in pharmaceutical preparations and the results agreed with the values obtained by the pharmacopoeia method.

A fluoroimmunosensing device which was based on ferulic acid (FA)/horseradish peroxidase system for the detection of Schistosoma japonicum antibody (SjAb) has been developed. To circumvent the difficulty of regeneration of immunocomposite surface, a natural chitosan-epoxy resin matrix was used for the immobilization of SjAg. The surface of the immunocomposite layer reacted was easily regenerated by simple polishing. The renewed surface served as a platform for the competitive immuno-reaction of HRP-SjAb and SjAb with SjAg immobilized at the support body surface and for enzymatic reaction. A novel fluorescent substrate ferulic acid for HRP, which is relatively stable toward H 2 O 2 , has been adapted in the proposed fluorometric enzyme immunosensing system. FA can been catalyzed to produce a non-fluorescent species. The amount of HRP-SjAb bound to the aforementioned renewable surface layer, which is related to the content of SjAb in samples could be quantitized by measuring the decrease of fluorescence of FA induced by HRP-SjAb. The chitosan incorporated in matrix is favorable for the amplification of this sensing system due to the electrostatic reaction with FA. The proposed method showed a linear response ranging from 45 to 150 ng ml −1 , with an improved detection limit of 45 ng ml −1 . The method has been employed to determine SjAb in serum samples.

Poly(2-macaptobenzimidazole) (PMBI) films are prepared at the gold electrode surface by electropolymerization using imprinting technology and the target analyte cholesterol is used as the template. A cholesterol-selective sensor based on PMBI film was employed in conjunction with differential pulse voltammetry (DPV) and ferricyanide as mediator. Concentration of cholesterol up to 100 microM could be detected with a linear determination range up to 20 microM and a detection limit of 0.7 microM. The molecular imprinting approach offers a relatively nice selectivity for the sensor toward cholesterol with respect to common coexisting substances. The method is simple and the stability of the electrode prepared is satisfactory. The results of this research show the feasibility of using molecular imprinting methodology for preparing sensing devices for analytes that are electrochemically inactive.

An immunosensing system for Schistosoma Japonicum antibody (SjAb) assay has been developed which is useful for the diagnosis of schistosomaisis. To circumvent the difficulty of regeneration of the immunosensing device, the sol-gel technique is used which results in a considerable retention of the activity of the encapsulated antigen (SjAb) and easily diffusing into the pores of the polymeric silica matrix. The surface of the immunosensing device prepared can easily be renewed by simply polishing. The regenerated surface serves as a platform for the competitive immuno-reaction of HRP-SjAb and SjAb with SjAg bound at the surface. By using 3, 3′, 5, 5′-tetramethylbenzidine (TMB) as the substrate, the amount of HRP-SjAb bound is quantitated fluorimetrically, which is in turn related with the SjAb content. An amplification effect is obtained by using the enzymatic reaction, and an improved detection limit of 4.5 ng ml−1 is thus realized. The optimum analytical conditions such as pH, amount of the labeled antibody and flow rates of substrate carrier solution were established. The immunosensing procedure shows a pseudo linear response range from 4.5 to 55 ng ml−1. The proposed procedure has been employed to determine SjAb in serum samples.