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A simple but effective method for the detection of miRNAs was proposed by integrating exonuclease-III assisted target recycling amplification and repeated-fishing strategy. In the proposed method, exonuclease-III assisted target recycling amplification reaction is adopted to produce a large amount of DNA fragments with fluorescence group at its 5′ end in the presence of the target miRNA, which are then repeatedly fished out from the reaction mixture by a gold foil modified with a capture probe and transferred into a so-called ‘product tube’. The amount of the target miRNA can then be determined from the fluorescence measurement of the solution in the ‘product tube’. Application to the detection of miRNA-155 in samples of KH-2 and BRSA-2B cells revealed that the proposed method could achieve sensitive and accurate quantification of the target miRNA with a limit of detection of 36 fM and recovery rates in the range from 96.2% to 105%. Its simplicity, sensitivity and resistance to possible fluorescence interferences in complex biological samples make the proposed method a potentially competitive alternative for miRNAs detection in complex biological samples.

Luminescent nanoclusters (NCs) have attracted much attention because of their good photostability and low toxicity, however, the low quantum yield is still a deficiency, and many increasing efforts are being devoted to enhance the luminescence intensity of NCs. In this paper, a method of enhancing the fluorescent signal of gold-silver nanoclusters (AuAgNCs) by photonic crystals (PhCs) was proposed. The fluorescent intensity of AuAgNCs on PhCs can be enhanced 8.0-fold in comparison to the control sample without PhCs. Furthermore, a novel fluorescence sensor of AuAgNCs based on PhCs is used for the sensitive and selective detection of Hg2+ ion in the aqueous solution, the detection limit is 0.35 nM due to the PhCs enhancement effect for the fluorescence. This proposed method may not only develop a highly sensitive method for determination of Hg2+ ion, but also expand the application of AuAgNCs in ultra-trace analysis.

Here, we report a novel fluorescence method for the highly selective and sensitive detection of RNase H by combining the use of a dual-pyrene-labeled DNA/RNA duplex with supramolecular inclusion-enhanced fluorescence. Initially, the probe is in the “off” state due to the rigidness of the double-stranded duplex, which separates the two pyrene units. In the presence of RNase H, the RNA strand of the DNA/RNA duplex will be hydrolyzed, and the DNA strand transforms into a hairpin structure, bringing close the two pyrene units which in turn enter the hydrophobic cavity of a γ-cyclodextrin. As a result, the pyrene excimer emission is greatly enhanced, thereby realizing the detection of RNase H activity. Under optimal conditions, RNase H detection can be achieved in the range from 0.08 to 4 U/mL, with a detection limit of 0.02 U/mL.

A novel soft strategy for combination and partition of mass spectra data recorded at different fragmentor voltages in full scan mode of a mass spectrometer was developed to generate abundant multi-way data. It is the first time that non-linear four-way and combined three-way LC-MS data have been obtained simultaneously in a single chromatographic run. This strategy ensures that each analyte can be ionized and detected at the most appropriate MS conditions (ionization modes, fragmentor voltages) and avoids a hard chromatographic segmentation in subsequent chemometric analysis. Two different experimental datasets were analyzed to validate the feasibility and applicability of this strategy. Some simple pretreatments were carried out before LC-MS analysis to prevent potential matrix effects. Proper chemometric tools were used to resolve three-way (partitioned data) and enhanced three-way LC-MS (combined data) data, respectively. The method was assessed by comparing the analytical results obtained from the same chemometric algorithm with both combined and partitioned datasets: (1) the combined data provided the best global overall resolution, higher sensitivity and more reliable results, (2) the partitioned data provided higher selectivity for some specific analytes. The results showed that the developed method could be a soft and ingenious tool to handle the unordered but information-rich raw LC-MS data. Moreover, the proposed strategy could take extra analytical advantages in terms of higher sensitivity and more reliable quantitative results when compared with LC-MS (with single fragmentor voltage) strategy and showed nearly the same capability in analytical quality as classic LC-MS/MS method.

This paper proposes a flexible and novel strategy that alternating trilinear decomposition (ATLD) method combines with two-dimensional linear discriminant analysis (2D-LDA). The developed strategy was applied to three-way chemical data for the characterization and classification of samples. In order to confirm the methodology performances of characterization and classification, a series of simulated three-way data arrays and a real-life EEMs data set involving the characterization and classification of tea samples according to the tea varieties were subjected to ATLD-2DLDA analysis. Further, the obtained results were compared with those obtained by using LDA based on relative concentrations of ATLD (ATLD-LDA), discriminant analysis by N-way partial least square (N-PLS-DA) and 2D-LDA method. For the simulated data sets with respect to different levels of noise and class overlap as well as number of groups, the ATLD-2DLDA always obtains superior classification performances than the ATLD-LDA, 2D-LDA and N-PLS-DA methods. Regarding the real EEMs data set of tea samples, the proposed methodology not only could provide a chemically meaningful model of the data for characterizing the different tea varieties, but also achieved the best correct classification rate (100%) for the test samples, compared with the results of ATLD-LDA (83.9%), 2D-LDA (90.3%) and N-PLS-DA (90.3%). These results demonstrated that the proposed methodology was indeed a feasible and reliable tool for characterization and classification of three-way chemical data arrays in a flexible and accurate manner.

PEBBLE (probe encapsulated by biologically localized embedding) nanosensor encapsulating an intensity-based fluorescence indicator and an inert reference fluorescence dye inside the pores of stable matrix can be used as a generalized wavelength-ratiometric probe. However, the lack of an efficient quantitative model render the choices of inert reference dyes and intensity-based fluorescence indicators used in PEBBLEs based generalized wavelength-ratiometric probes rather limited. In this contribution, an extended quantitative fluorescence model was derived specifically for generalized wavelength-ratiometric probes based on PEBBLE technique (QFM GRP ) with a view to simplify the design of PEBBLEs and hence further extend their application potentials. The effectiveness of QFM GRP has been tested on the quantitative determination of free Ca 2+ in both simulated and real turbid media using a Ca 2+ sensitive PEBBLE nanosensor encapsulating Rhod-2 and eosin B inside the micropores of stable polyacrylamide matrix. Experimental results demonstrated that QFM GRP could realize precise and accurate quantification of free Ca 2+ in turbid samples, even though there is serious overlapping between the fluorescence excitation peaks of eosin B and Ca 2+ bound Rhod-2. The average relative predictive error value of QFM GRP for the test simulated turbid samples was 5.9%, about 2–4 times lower than the corresponding values of partial least squares calibration model and the empirical ratiometric model based on the ratio of fluorescence intensities at the excitation peaks of Ca 2+ bound Rhod-2 and eosin B. The recovery rates of QFM GRP for the real and spiked turbid samples varied from 93.1% to 101%, comparable to the corresponding results of atomic absorption spectrometry.

Determination of benzo[a]pyrene (BaP) in cigarette smoke can be very important for the tobacco quality control and the assessment of its harm to human health. In this study, mid-infrared spectroscopy (MIR) coupled to chemometric algorithm (DPSO-WPT-PLS), which was based on the wavelet packet transform (WPT), discrete particle swarm optimization algorithm (DPSO) and partial least squares regression (PLS), was used to quantify harmful ingredient benzo[a]pyrene in the cigarette mainstream smoke with promising result. Furthermore, the proposed method provided better performance compared to several other chemometric models, i.e., PLS, radial basis function-based PLS (RBF-PLS), PLS with stepwise regression variable selection (Stepwise-PLS) as well as WPT-PLS with informative wavelet coefficients selected by correlation coefficient test (rtest-WPT-PLS). It can be expected that the proposed strategy could become a new effective, rapid quantitative analysis technique in analyzing the harmful ingredient BaP in cigarette mainstream smoke.

The sensitive detection of tumor proto-oncogenes is indispensable because the early diagnosis and accurate treatment of genetic diseases is the key guarantee of patients' health. In this study, we proposed a novel palindromic molecular beacon (PMB) that it bases on the signal amplification strategy for ultrasensitive detection of Kras gene codon 12. PMB is designed to have two palindromic fragments at its two ends, one of which is locked via folding into a hairpin structure and the other promotes the formation of PMB duplex via intermolecular self-hybridization. Target DNA can hybridize to the loop portion of PMB and release the palindromic fragment at the 3’ end. Within the PMB duplex, the two palindromic fragments released hybridize with each other and serve as polymerization primer responsible for the strand-displacement amplification (SDA). Namely, hybridized target DNA can be displaced and initiates the next round of reactions, making the polymerization/displacement/hybridization process go forward circularly. As a result, a large number of polymerization products are produced, dramatically enhancing optical signal. Because primer hybridization and polymerization-based displacement occur within PMB duplex, the reaction process is called intramolecular strand-displacement amplification (ISDA). Via utilizing the newly-proposed PMB-based ISDA strategy, the target K-ras gene could be detected down to 10 pM with a wide response range of 1 × 10−11-1.5 × 10−7 M, and point mutations are easily distinguished, realizing the ultrasensitive, highly selective detection of K-ras gene. This impressive sensing paradigm demonstrates a new concept of signal amplification for the detection of disease-related genes only via using a simple way to efficiently amplify optical signal.

Loop-mediated isothermal amplification (LAMP) is a useful platform for nucleic acids detection in point-of-care (POC) situations, and development of single-step, close-tube LAMP reactions for specific detection of single nucleotide mutations (SNMs) remains a challenge. We develop a novel primer-activatable LAMP (PA-LAMP) strategy that enables highly specific and sensitive SNM detection using single-step, close-tube reactions. This strategy designs a terminal-blocked inner primer with a ribonucleotide insertion, which is cleaved and activated specifically to perfectly matched targets by ribonuclease (RNase) H2, to realize efficient amplification of mutant genes. It has shown dynamic responses of mutant target in a linear range from 220 aM to 22 pM with a lowest detectable concentration of 22 aM. It also demonstrates very high specificity in identifying the mutant in a large excess of the wild-type with a discrimination ratio as high as ∼10,000. It has been successfully applied to mutation detection of genomic DNA in tumor cells. The PA-LAMP strategy provides a useful, portable and affordable POC platform for highly sensitive and specific detection of genetic mutations in clinical applications.

In this contribution, surface-enhanced Raman spectroscopy (SERS) based on conical holed glass substrates deposited with silver colloids was reported for the first time. It combines the advantages of both dry SERS assays based on plane films deposited with silver colloids and wet SERS assays utilizing cuvettes or capillary tubes. Compared with plane glass substrates deposited with silver colloids, the conical holed glass substrates deposited with silver colloids exhibited five-to ten-folds of increase in the rate of signal enhancement, due to the internal multiple reflections of both the excitation laser beam and the Raman scattering photons within conical holes. The application of conical holed glass substrates could also yield significantly stronger and more reproducible SERS signals than SERS assays utilizing capillary tubes to sample the mixture of silver colloids and the solution of the analyte of interest. The conical holed glass substrates in combination with the multiplicative effects model for surface-enhanced Raman spectroscopy (MEMSERS) achieved quite sensitive and precise quantification of 6-mercaptopurine in complex plasma samples with an average relative prediction error of about 4% and a limit of detection of about 0.02 μM using a portable i-Raman 785H spectrometer. It is reasonable to expect that SERS technique based on conical holed enhancing substrates in combination with MEMSERS model can be developed and extended to other application areas such as drug detection, environmental monitoring, and clinic analysis, etc.

There is a great deal of interest in decompositions of multilinear component models in the field of multi-way calibration, especially the three-way case. A flexible novel trilinear decomposition algorithm of the trilinear component model as a modification of an alternating least squares algorithm for three-way calibration is proposed. The proposed algorithm (constrained alternating trilinear decomposition, CATLD) is based on an alternating approximate least-squares scheme, in which two extra terms are added to each loss function, making it more efficient and flexible. The analysis of simulated three-way data arrays shows that it converges fast, is insensitive to initialization, and is insensitive to the overestimated number of components used in the decomposition. The analysis of real excitation–emission matrix (EEM) fluorescence and real high performance liquid chromatography–photodiode array detection (HPLC–DAD) data arrays confirms the results of the simulation studies, and shows that the proposed algorithm is favorable not only for EEMs but also for HPLC–DAD data. The three-way calibration method based on the CATLD algorithm is very efficient and flexible for direct quantitative analysis of multiple analytes of interest in complex systems, even in the presence of uncalibrated interferents and varying background interferents. Additionally, a theoretical extension of the proposed algorithm to the multilinear component model (constrained alternating multilinear decomposition, CAMLD) is developed.

β-blockers are the first-line therapeutic agents for treating cardiovascular diseases and also a class of prohibited substances in athletic competitions. In this work, a smart strategy that combines three-way liquid chromatography-mass spectrometry (LC-MS) data with second-order calibration method based on alternating trilinear decomposition (ATLD) algorithm was developed for simultaneous determination of ten β-blockers in human urine and plasma samples. This flexible strategy proved to be a useful tool to solve the problems of overlapped peaks and uncalibrated interferences encountered in quantitative LC-MS, and made the multi-targeted interference-free qualitative and quantitative analysis of β-blockers in complex matrices possible. The limits of detection were in the range of 2.0×10(-5)-6.2×10(-3) μg mL(-1), and the average recoveries were between 90 and 110% with standard deviations and average relative prediction errors less than 10%, indicating that the strategy could provide satisfactory prediction results for ten β-blockers in human urine and plasma samples only using liquid chromatography hyphenated single-quadrupole mass spectrometer in full scan mode. To further confirm the feasibility and reliability of the proposed method, the same batch samples were analyzed by multiple reaction monitoring (MRM) method. T-test demonstrated that there are no significant differences between the prediction results of the two methods. Considering the advantages of fast, low-cost, high sensitivity, and no need of complicated chromatographic and tandem mass spectrometric conditions optimization, the proposed strategy is expected to be extended as an attractive alternative method to quantify analyte(s) of interest in complex systems such as cells, biological fluids, food, environment, pharmaceuticals and other complex samples.

Uracil-DNA glycosylase (UDG) plays essential roles in base excision repair (BER) pathway by eliminating uracil from DNA to sustain the genome integrity. Sensitive detection of UDG activity is of great significance in the study of many fundamental biochemical processes and clinical applications. We develop a label-free method for UDG activity detection using stem-loop primer-mediated exponential amplification (SPEA). In the presence of active UDG, the uracil base in helper hairpin probe (HP) can be excised to generate an abasic site (AP site), which can be cleaved by endonuclease IV (Endo IV) with a blocked primer released. This primer then triggers the strand displacement reaction to produce a dumb-bell structure DNA, which can initiate a loop-mediated isothermal amplification (LAMP) reaction. This reaction generates a large number of long double-strand DNA replicates, which can be stained by SYBR Green (SG) I to deliver enhanced fluorescence for quantitative detection of UDG activity. A linear range from 0.001 U/mL to 1 U/mL and a detection limit down to 0.00068 U/mL are achieved. This strategy has also been demonstrated for UDG assay in complex cell lysates, implying its great potential for UDG based clinical diagnostics and therapeutics.

Existing strategies for detecting nicotinamide adenine dinucleotide (NAD + ) or other cofactors are commonly cumbersome and moderate sensitive. We report a novel DNAzyme-based visual assay strategy for NAD + based on ligase-mediated inhibition of the strand displacement amplification (SDA). In the presence of NAD + , the SDA can be inhibited by the ligase reaction of two primers, which can initiate the SDA reaction in the case of no ligation, resulting in a dramatically decreasing yield of the SDA product, a G-quadruplex DNAzyme that can quantitatively catalyze the formation of a colored product. Therefore, the quantitative analysis for NAD + can be achieved visually with high sensitivity. The developed strategy provides a simple colorimetric approach with high selectivity against most interferences and a detection limit as low as 50 pM. It also provides a universal platform for investigating cofactors or other related small molecules as well as quantifying the activity of DNA ligases.

Engineered nucleic acid probes containing recognition and signaling functions find growing interest in biosensor design. In this paper, we developed a novel electrochemical biosensor for sensitive and selective detecting of Hg(2+) based on a bifunctional oligonucleotide signal probe combining a mercury-specific sequence and a G-quadruplex (G4) sequence. For constructing the electrochemical Hg(2+) biosensor, a thiolated, mercury-specific oligonucleotide capture probe was first immobilized on gold electrode surface. In the presence of Hg(2+), a bifunctional oligonucleotide signal probe was hybridized with the immobilized capture probe through thymine-mercury(II)-thymine interaction-mediated surface hybridization. The further interaction between G4 sequence of the signal probe and hemin generated a G4-hemin complex, which catalyzed the electrochemical reduction of hydrogen peroxide, producing amplified readout signals for Hg(2+) interaction events. This electrochemical Hg(2+) biosensor was highly sensitive and selective to Hg(2+) in the concentration of 1.0 nM to 1 μM with a detection limit of 0.5 nM. The new design of bifunctional oligonucleotide signal probes also provides a potential alternative for developing simple and effective electrochemical biosensors capable of detecting other metal ions specific to natural or artificial bases.

Due to the ubiquity and essential of the proteins in all living organisms, the identification and quantification of disease-specific proteins are particularly important. Because the conformational change of aptamer upon its target or probe/target/probe sandwich often is the primary prerequisite for the design of an electrochemical aptameric assay system, it is extremely difficult to construct the electrochemical aptasensor for protein assay because the corresponding aptamers cannot often meet the requirement. To circumvent the obstacles mentioned, an electronic channel switching-based (ECS) aptasensor for ultrasensitive protein detection is developed. The essential achievement made is that an innovative sensing concept is proposed: the hairpin structure of aptamer is designed to pull electroactive species toward electrode surface and makes the surface-immobilized IgE serve as a barrier that separates enzyme from its substrate. It seemingly ensures that the ECS aptasensor exhibits most excellent assay features, such as, a detection limit of 4.44 × 10−6 μg mL−1 (22.7 fM, 220 zmol in 10-μL sample) (demonstrating a 5 orders of magnitude improvement in detection sensitivity compared with classical electronic aptasensors) and dynamic response range from 4.44 × 10−6 to 4.44 × 10−1 μg mL−1. We believe that the described sensing concept here might open a new avenue for the detection of proteins and other biomacromolecules.

A novel quadrilinear decomposition algorithm for four-way calibration (third-order tensor calibration), which was called as regularized self-weighted alternating quadrilinear decomposition (RSWAQLD), has been developed in this work. It originates from the alternating trilinear decomposition (ATLD) algorithm, inherits the philosophy behind self-weighting operation from the self-weighted alternating trilinear decomposition (SWATLD) algorithm. The RSWAQLD algorithm is based on a nearby least-squares scheme, in which two extra terms are added to each loss function, making it more stable and flexible. Experiment shows that RSWAQLD has the features of fast convergence and being insensitive to the excess estimated factors in the model. Owing to its unique optimizing approach, RSWAQLD is much more efficient than four-way PARAFAC. Moreover, the performance of RSWAQLD is quit stable as the number of factors used in calculation varies (as long as it is no less than the true number of factors). Such a feature will simplify the analysis of four-way data arrays, since it is unnecessary to spend a lot of time and effort on accurately determining the appropriate number of factors in the matrix. In addition, the result of four-way fluorescence excitation-emission-pH data, as well as that of simulated data, illustrated that RSWAQLD can not only remain the "higher-order advantage" but also provide a satisfying result even in high collinear systems.

In this paper, for the first time, Cu nanoparticles (CuNPs) were prepared by seed-mediated growth method with Au nanoparticles (AuNPs) playing the role of seeds. Carbon nanotubes (CNTs) and AuNPs were first dropped on the surface of glassy carbon (GC) electrode, and then the electrode was immersed into growth solution that contained CuSO(4) and hydrazine. CuNPs were successfully grown on the surface of the CNTs. The modified electrode showed a very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium, which was utilized as the basis of the fabrication of a nonenzymatic biosensor for electrochemical detection of glucose. The biosensor can be applied to the quantification of glucose with a linear range covering from 1.0×10(-7) to 5×10(-3)M and a low detection limit of 3×10(-8)M. Furthermore, the experiment results also showed that the biosensor exhibited good reproducibility and long-term stability, as well as high selectivity with no interference from other oxidable species.

The metabolic coenzymes reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) are the primary electron donor and acceptor respectively, participate in almost all biological metabolic pathways. This study develops a novel method for the quantitative kinetic analysis of the degradation reaction of NADH and the formation reaction of FAD in human plasma containing an uncalibrated interferent, by using three-way calibration based on multi-way fluorescence technique. In the three-way analysis, by using the calibration set in a static manner, we directly predicted the concentrations of both analytes in the mixture at any time after the start of their reactions, even in the presence of an uncalibrated spectral interferent and a varying background interferent. The satisfactory quantitative results indicate that the proposed method allows one to directly monitor the concentration of each analyte in the mixture as the function of time in real-time and nondestructively, instead of determining the concentration after the analytical separation. Thereafter, we fitted the first-order rate law to their concentration data throughout their reactions. Additionally, a four-way calibration procedure is developed as an alternative for highly collinear systems. The results of the four-way analysis confirmed the results of the three-way analysis and revealed that both the degradation reaction of NADH and the formation reaction of FAD in human plasma fit the first-order rate law. The proposed methods could be expected to provide promising tools for simultaneous kinetic analysis of multiple reactions in complex systems in real-time and nondestructively.

The detection of bacterial spores requires the capability of highly sensitive and biocompatible probes. This report describes the findings of an investigation of surface-enhanced Raman spectroscopic (SERS) detection of Bacillus subtilis spores using gold-nanoparticle (Au NP) based substrates as the spectroscopic probe. The SERS substrates are shown to be highly sensitive for the detection of B. subtilis spores, which release calcium dipicolinate (CaDPA) as a biomarker. The SERS bands of CaDPA released from the spores by extraction using nitric acid provide the diagnostic signal for the detection, exhibiting a limit of detection (LOD) of 1.5 × 10 9 spores L −1 (or 2.5 × 10 −14 M). The LOD for the Au NP based substrates is quite comparable with that reported for Ag nanoparticle based substrates for the detection of spores, though the surface adsorption equilibrium constant is found to be smaller by a factor of 1–2 orders of magnitude than the Ag nanoparticle based substrates. The results have also revealed the viability of SERS detection of CaDPA released from the spores under ambient conditions without extraction using any reagents, showing a significant reduction of the diagnostic peak width for the detection. These findings have demonstrated the viability of Au NP based SERS substrates for direct use with high resolution and sensitivity as a biocompatible probe for the detection of bacterial spores.

A novel application of second-order calibration method based on an alternating penalty trilinear decomposition (APTLD) algorithm is presented to treat the data from high performance liquid chromatography-diode array detection (HPLC-DAD). The method makes it possible to accurately and reliably analyze atrazine (ATR), ametryn (AME) and prometryne (PRO) contents in soil, river sediment and wastewater samples. Satisfactory results are obtained although the elution and spectral profiles of the analytes are heavily overlapped with the background in environmental samples. The obtained average recoveries for ATR, AME and PRO are 99.7 ± 1.5, 98.4 ± 4.7 and 97.0 ± 4.4% in soil samples, 100.1 ± 3.2, 100.7 ± 3.4 and 96.4 ± 3.8% in river sediment samples, and 100.1 ± 3.5, 101.8 ± 4.2 and 101.4 ± 3.6% in wastewater samples, respectively. Furthermore, the accuracy and precision of the proposed method are evaluated with the elliptical joint confidence region (EJCR) test. It lights a new avenue to determine quantitatively herbicides in environmental samples with a simple pretreatment procedure and provides the scientific basis for an improved environment management through a better understanding of the wastewater–soil–river sediment system as a whole.

A novel piezoelelctric biosensor has been developed for cholera toxin (CT) detection based on the analyte-mediated surface-agglutination of ganglioside (GM1)-functionalized liposomes. To achieve a CT-specific agglutination at the surface, the gold electrode is modified by a GM1-functionalized supported lipid membrane via spontaneous spread of the liposomes on a self-assembled monolayer of a long-chain alkanethiol. In the presence of CT, the GM1-incorporated liposomes in assay medium will rapidly specifically agglutinate at the electrode surface through the binding of CT to GM1 on the electrode surface and the liposome interface. This results in an enormous mass loading on the piezoelelctric crystal as well as a significant increase of density and viscosity at the interface, thereby generating a decrease in frequency of the piezoelelctric crystal. The combination of mass loading with interfacial change in the surface-agglutination reaction allows the developed piezoelelctric biosensor to show substantial signal amplification in response to the analyte CT. The detection limit can be achieved as low as 25 ng mL −1 CT. This is the first demonstration on CT detection based on specific surface-agglutination of GM1-modified liposomes. The supported lipid layer based sensing interface can be prepared readily and renewably, making the developed technique especially useful for simple, reusable and sensitive determination of proteins.

In this paper, for the first time, we introduced the seed-mediated method to the growth of cobalt hexacyanoferrate nanoparticles (CoNPs), using 3.5 nm gold nanoparticles as seeds and multiwalled carbon nanotubes (MWCNTs) as growth scaffold which would both show synergistic action toward the reduction of H2O2. Via gold seeds, the one-step fabrication of CoNPs on the glassy carbon electrode is simple without any linking reagents, which will ingeniously exert the electrochemical properties of cobalt hexacyanoferrate. Combined with glucose oxidase, the sensing surface is applied as a biosensor for glucose. The growth of CoNPs is a chemical deposition process around the small Au nanoseed particles. The nanoseeds bridge the CoNPs and CNTs to form a smart nanocomposite. Spherical CoNPs have a relatively moderate dispersion on the three-dimensional network of CNTs with relatively even diameter ca. 100 nm. Whereas, in the control experiments without gold seeds cobalt hexacyanoferrate can only form continuous films, of which the size is far from nanolevel and the catalytic ability is poor. The synthesis and fabrication/modification of CoNPs are simple and fast without prior preparation of CoNPs and lengthy process of cross-linking. The amount of the seeds and CNTs, growth time and concentration of growth solution were investigated. Scanning electron microscopy (SEM) and electrochemical method were used.

Two second-order calibration methods based on the parallel factor analysis (PARAFAC) and the alternating penalty trilinear decomposition (APTLD) method, have been utilized for the direct determination of terazosin hydrochloride (THD) in human plasma samples, coupled with the excitation–emission matrix fluorescence spectroscopy. Meanwhile, the two algorithms combing with the standard addition procedures have been applied for the determination of terazosin hydrochloride in tablets and the results were validated by the high-performance liquid chromatography with fluorescence detection. These second-order calibrations all adequately exploited the second-order advantages. For human plasma samples, the average recoveries by the PARAFAC and APTLD algorithms with the factor number of 2 (N = 2) were 100.4 ± 2.7% and 99.2 ± 2.4%, respectively. The accuracy of two algorithms was also evaluated through elliptical joint confidence region (EJCR) tests and t-test. It was found that both algorithms could give accurate results, and only the performance of APTLD was slightly better than that of PARAFAC. Figures of merit, such as sensitivity (SEN), selectivity (SEL) and limit of detection (LOD) were also calculated to compare the performances of the two strategies. For tablets, the average concentrations of THD in tablet were 63.5 and 63.2 ng mL−1 by using the PARAFAC and APTLD algorithms, respectively. The accuracy was evaluated by t-test and both algorithms could give accurate results, too.

Multi-way data analysis and tensorial calibration are gaining widespread acceptance with the rapid development of modern analytical instruments. In recent years, our group working in State Key Laboratory of Chemo/Biosensing and Chemometrics in Hunan University has carried out exhaustive scientific research work in this area, such as building more canonical symbol systems, seeking the inner mathematical cyclic symmetry property for trilinear or multilinear decomposition, suggesting a series of multi-way calibration algorithms, exploring the rank estimation of three-way trilinear data array and analyzing different application systems. In this present paper, an overview from second-order data to third-order data covering about theories and applications in analytical chemistry has been presented.

An ultrasensitive piezoelectric method for the detection of the aflatoxin B 1 (AFB 1 ) based on the indirect competitive immunoassay and the biocatalyzed deposition amplification has been developed. In this method, the quartz crystal surface was coated with a self-assembled monolayer of 3-mercaptopropionic acid (MPA) for covalently immobilization of the BSA-AFB 1 conjugate, which could compete with the free AFB 1 for binding to the anti-AFB 1 antibody (MsIgG). After the competitive immunoreaction, the horseradish peroxidase (HRP) labeled goat anti-mouse IgG (G-Anti-MsIgG) was introduced into the detection cell to combine with the anti-AFB 1 antibody on the crystal surface. The enzyme labeled G-Anti-MsIgG as a biocatalyst could accelerate the oxidation of 4-chloro-1-naphthol by H 2 O 2 to yield the insoluble product benzo-4-chlorohexadienone on the surface of quartz crystal microbalance (QCM), resulting in a mass increase that was reflected by a decrease in the resonance frequency of the QCM. The proposed approach could allow for the determination of AFB 1 in the concentration range of 0.01–10.0 ng mL −1 . Furthermore, several artificially contaminated milk samples were analyzed with good recoveries obtained, which demonstrated the suitability of the proposed method for detecting AFB 1 .

In the traditional framework of multivariate spectroscopic calibration, the most popular method, partial least squares (PLS), shrinks the regression coefficients based on the information of training sample concentrations. Motivated by the concept of parallel calibration, the second direction for shrinkage of regression coefficients, the direction towards unknown sample spectra is investigated in this paper. A different multivariate calibration method, parallel calibration model based on partial least squares, PCPLS is proposed. With both theoretical support and analysis of some real data sets, it is demonstrated that the second shrinkage direction is at least as natural and necessary as the traditional one. An interesting difference of the proposed method from traditional methods is the involvement of unknown sample spectra and consideration of their error in the training process. Some new related problems and potential applications of this method are also briefly discussed.

An optical sensor for mercury ion (Hg(2+)), based on quenching the fluorescence of the sensing reagent porphyrin immobilized in plasticized poly(vinyl chloride) (PVC) membrane, has been developed. The responses to mercury ion were compared for the sensors modified with three porphyrin compounds including 5,10,15,20-tetraphenylporphyrin (TPP), tetra(p-dimethylaminophenyl)porphyrin (TDMAPP) and tetra(N-phenylpyrazole) porphyrin (TPPP). Among them, TDMAPP showed the most remarkable response to Hg(2+). The drastic decrease of the TDMAPP fluorescence intensity was attributed to the formation of a complex between TDMAPP and Hg(2+), which has been utilized as the fabrication basis of a Hg(2+)-sensitive fluorescence sensor. The analytical performance characteristics of the TDMAPP modified sensor was investigated. The response mechanism, especially involving the response difference of three porphyrin compounds, was discussed in derail. The sensor can be applied to the quantification of Hg(2+) with a linear range covering from 4,0 x 10(-8) mol L(-1) to 4.0 x 10(-6) mol L(-1). The limit of detection was 8.0 x 10(-9) mol L(-1). The sensor exhibited excellent reproducibility, reversibility and selectivity. Also, the TDMAPP-based sensor was Successfully used for the determination of Hg(2+) in environmental water samples. (C) 2009 Elsevier B.V. All rights reserved.

A sensitive excitation-emission fluorescence method was proposed to determine testosterone propionate (TP) in several cosmetics with the aid of second-order calibration methods based on the self-weighted alternating trilinear decomposition (SWATLD) and parallel factor analysis (PARAFAC) algorithms. TP can be transformed into a highly fluorescent derivative through oxidation reaction with concentrated sulfuric acid (H 2 SO 4 ). Both algorithms have been recommended to enhance the selectivity and attain TP concentration in cosmetics free from interference from potential interfering matrix contaminants introduced during simple cosmetic pretreatment procedure, even in the presence of other homogeneous drugs. Satisfactory results have been achieved for TP in complicated cosmetics, fully exploiting “second-order advantage”. The correlation coefficients of TP obtained by using both SWATLD and PARAFAC with N = 3 are 0.9968 and 0.9974, and the average recoveries, 99.3 ± 4.7% and 101.3 ± 5.9%, respectively. Furthermore, in order to investigate the performance of the proposed methods, some statistical parameters and figures of merit of SWATLD and PARAFAC, i.e., sensitivity (SEN), selectivity (SEL) and limit of detection (LOD) were evaluated, and the accuracy of both algorithms was also validated by the elliptical joint confidence region (EJCR) test.

Preprocessing of raw near-infrared (NIR) spectral data is indispensable in multivariate calibration when the measured spectra are subject to significant noises, baselines and other undesirable factors. However, due to the lack of sufficient prior information and an incomplete knowledge of the raw data, NIR spectra preprocessing in multivariate calibration is still trial and error. How to select a proper method depends largely on both the nature of the data and the expertise and experience of the practitioners. This might limit the applications of multivariate calibration in many fields, where researchers are not very familiar with the characteristics of many preprocessing methods unique in chemometrics and have difficulties to select the most suitable methods. Another problem is many preprocessing methods, when used alone, might degrade the data in certain aspects or lose some useful information while improving certain qualities of the data. In order to tackle these problems, this paper proposes a new concept of data preprocessing, ensemble preprocessing method, where partial least squares (PLSs) models built on differently preprocessed data are combined by Monte Carlo cross validation (MCCV) stacked regression. Little or no prior information of the data and expertise are required. Moreover, fusion of complementary information obtained by different preprocessing methods often leads to a more stable and accurate calibration model. The investigation of two real data sets has demonstrated the advantages of the proposed method.

We report the synthesis of a novel looped enzyme-polyamidoamine nanocomposite with high enzyme loading density and long-term retention of bioactivity. The horseradish peroxidase (HRP) is first immobilized on fourth-grade (G4) poly(amidoamine) (PAMAM) dendrimer to form relatively a small enzyme-PAMAM composite, which is allowed to grow up into a larger one. The looped horseradish peroxidase-polyamidoamine (HRP-PAMAM) nanohybrid was characterized by TEM. The material obtained shows promising features as applied to the fabrication of high sensitive and long lifetime biosensors. In the presence of the hydroquinone mediator in the solution, the immobilized HRP exhibited excellent electro-catalytical response to H2O2. Under the optimal conditions, the resulting biosensor showed a linear response to H2O2 over a concentration range from 3.1x10(-6) to 2.0x10(-3) mol L(-1) with a sensitivity of 0.36 A L mol(-1) cm(-2) and a detection limit of 8.0x10(-7) mol L(-1). The sensitivity of the sensor response maintained over 70% of the original over 10 weeks. The catalytic activity of the looped enzyme-PAMAM nanohybrid form of HRP enzyme was obviously stabilized. As an extension, bienzyme sensor modified with glucose oxidase and HRP enzymatic PAMAM nanocomposites was constructed. The sensor exhibited improved performance and can be applied to the detection of glucose in real samples.

A novel and sensitive electrochemical DNA biosensor based on nanoparticles ZrO 2 and multi-walled carbon nanotubes (MWNTs) for DNA immobilization and enhanced hybridization detection is described. The MWNTs/nano ZrO 2 /chitosan-modified glassy carbon electrode (GCE) was fabricated and oligonucleotides were immobilized to the GCE. The hybridization reaction on the electrode was monitored by differential pulse voltammetry (DPV) analysis using electroactive daunomycin as an indicator. Compared with previous DNA sensors with oligonucleotides directly incorporated on carbon electrodes, this carbon nanotube-based assay with its large surface area and good charge-transport characteristics increased DNA attachment quantity and complementary DNA detection sensitivity. The response signal increases linearly with the increase of the logarithm of the target DNA concentration in the range of 1.49 × 10 −10 to 9.32 × 10 −8 mol L −1 with the detection limit of 7.5 × 10 −11 mol L −1 ( S / N = 3). The linear regression equation is I = 32.62 + 3.037 log C DNA (mol L −1 ) with a correlation coefficient value of 0.9842. This is the first application of carbon nanotubes combined with nano ZrO 2 to the fabrication of an electrochemical DNA biosensor with a favorable performance for the rapid detection of specific hybridization.

This study reports a novel, simple and sensitive immunoassay using fluorescence quenching caused by gold nanoparticles coated with antibody. The method is based on a non-competitive heterogeneous immunoassay of human IgG conducted by the typical procedure of sandwich immunocomplex formation. Goat anti-human IgG was first adsorbed on polystyrene microwells, and human IgG analyte was captured by the primary antibody and then sandwiched by antibody labeled with gold nanoparticles. The sandwich-type immunocomplex was subsequently dissociated by the mixed solution of sodium hydroxide and trisodium citrate, the solution obtained, which contains gold nanoparticles coated with antibody, was used to quench fluorescence. The fluorescence intensity of fluorescein at 517 nm was inversely proportional to the logarithm of the concentration of human IgG in the dynamic range of 10-5000 ng mL(-1) with a detection limit of 4.7 ng mL(-1). The electrochemical experiments and the UV-vis measurements were applied to demonstrate whether the immunogold was dissociated completely and whether the gold nanoparticles aggregated after being dissociated, respectively. The proposed system can be extended to detect target molecules such as other kinds of antigen and DNA strands, and has broad potential applications in disease diagnosis.

A novel optical sensor based on covalent immobilization for picric acid assay has been described. To improve the stability of the sensor, a terminal double bond was attached to the fluorescent compound, 3-amino-9-ethylcarbazole (AEC), via methacryloyl chloride. The resultant compound, 3-(N-methacryloyl) amino-9-ethylcarbazole (MAEC) was copolymerized with 2-hydroxypropyl methacrylate on surface-modified quartz glass plates by UV irradiation. The resulting optical sensor (optode membrane) was used to determine picric acid based on fluorescence quenching. It shows a linear response toward picric acid in the concentration range of 9.33 x 10(-8) to 9.33 x 10(-5) mol l(-1), with rapid response, high stability and good selectivity to picric acid.

This paper describes a copper selective optical chemical sensor based on static quenching of the fluorescence of 2-(2′-hydroxyphenyl)benzoxazole entrapped in a poly(vinyl chloride) (PVC) membrane. The effect of the composition of the sensing membrane was studied, and experimental conditions were optimized. The sensors exhibit stable response over the concentration range from 4.0 × 10−8 M to 5.0 × 10−5 M Cu2+ at pH 4.0–6.5, and a high selectivity. The response time for Cu2+ with concentration ≤5 × 10−6 M is less than 7 min. The optode can be regenerated using 0.1 M HCl and acetate buffer solution. The sensor has been used for direct measurement of copper content in river water samples with a relative error less than 4% with reference to that obtained by atomic absorption spectrometry.

An approach to prepare novel glass-coated gold core-shell nanoparticles embedded with Raman active molecules has been developed. This strategy eliminates the need of a coupling agent and enables efficient embedding of most of commercially available Raman active dyes, even those with weak affinity to a gold surface. Our experiments have demonstrated the hypothesis that the glass encapsulation chemistry is based on the reaction between silanol groups hydrolyzed by TEOS and citrate anion groups adsorbed onto the gold nanoparticles leading to the formation of a silica layer through further reaction with silanol groups of other hydrolyzed TEOS. Furthermore, it has been demonstrated the potential of these novel nanoparticls as Raman tags in ultrasensitive immunoassays for human IgG antigen with a detection limit of 4.9 ng/ml.

A novel method of preparing fluorescence particle probe by emulsion polymerization with covalent immobilization of indicator dye was described. A terminal double bond was attached to 3-amino-9-ethylcarbazole (AEC) via methacryloyl chloride, and the resultant compound was copolymerized with butyl methacrylate. The obtained polymer particles were used as a fluorescence probe, which is almost free of dye leaching, and has higher photostability and lower toxicity in comparison with free AEC. This probe holds great potential for the applications in intracellular measurements. In present study the prepared probe was used for the determination of metronidazole. The results revealed that the probe showed good selectivity and had a linear response to the analyte in the range from 2.0 × 10−5 to 1.0 × 10−3 mol l−1 with a detection limit of 9.0 × 10−6 mol l−1.

In the resolution of overlapping chromatographic peaks, reliable information about the concentration windows of all chemical components is crucial for the success of many multivariate resolution methods. In this paper, taking the advantage of trilinearity that is intrinsic in many three-way data arrays, the trilinear evolving factor analysis (TEFA) is derived to establish a trilinear rank map for three-way multi-component chromatograms. With the information of local rank obtained from the trilinear rank map, selective region of each component can be determined. This provides the possibility to resolve the profiles of a single component one by one. It is shown that combining the local eluting information and the coupled vector resolution, a fast and reliable non-iterative resolution of the trilinear data array can be obtained. Simulated and real experimental results have demonstrated that the proposed method possesses the properties of easy implementation and excellent performance for the resolution of three-way multi-component chromatograms.

A new method based on cyclic accumulation of gold nanoparticles has been proposed for determinating human immunoglobulin G (IgG) by anodic stripping voltammetry. The dissociation reaction between dethiobiotin and avidin in the presence of biotin provides efficient means for the cyclic accumulation of gold nanoparticles used for the final analytical quantification. The immunoassay was conducted by following the typical procedure for sandwich-type immunoreaction. Goat anti-human IgG is immobilized on the wells of microtiter plates. The human IgG analyte is first captured by the primary antibody and then sandwiched by secondary antibody labeled with dethiobiotin. Avidin-Au solution was introduced to react with dethiobiotinylated antibody followed by adding of bioitin solution to wash it down. The dissociation of avidin-Au from dethiobiotinylated antibody was caused by displacing function of biotin to dethiobiotin. Making use of the ability of dethiobiotinylated antibody keeping its activity after the association/dissociation reaction, the alternatively treatment with avidin-Au and biotin solutions could realize cyclic accumulation of gold nanoparticles for ASV quantification. The anodic peak current increases gradually with the increasing accumulation cycles. Five cycles of accumulation are sufficient for the assay. The experiment conducted with a blank solution without addition of the analyte showed an extremely low background even with the number of accumulation cycles reached 10. The low background of the proposed method is a distinguished advantage providing a possibility for determination of at least 0.1 ng/ml human IgG. The RSD of the method is 9.57% for eight times determination of 1 ng/ml human IgG under the same conditions.

In the present work, we employed piecewise hyper-sphere modeling by particle swarm optimization (PHMPSO) which splits the dataset into subsets with desired linearity in each model for QSAR studies of a series of 2-aryl(heteroaryl)-2,5-dihydropyrazolo[4,3-c]quinolin-3-(3H)-ones (PQs) for their affinity to benzodiazepine receptor (BzR). The results were compared to those obtained by MLR modeling in a single model with the whole data set as well as in submodels based on K-means clustering analysis. It has been clearly shown that electronic descriptors and spatial descriptors play the important roles in the compounds’ affinity to BzR. In addition, the molecular density, the Y component of the principal moment of inertia, the magnitude and the Y component of the dipole moment of the molecules can detrimentally affect PQ analogue BzR affinity, while the X component of the dipole moment of the molecules can favorably affect compounds’ affinity.

In this paper, a new immunosensor has been proposed based on the receptor protein adsorbed directly on a porous gold film. The film was produced electrochemically on a glassy carbon electrode in 0.08 M hydrogen tetrachloroaurate solution containing 0.004 M lead acetate with applied potential of −0.5 V (versus Ag/AgCl) for 50 s. The assay was carried out based on a sandwich procedure. The impedance signals amplified by precipitation of an insoluble product on the electrode showed good linearity with the content of IgG in the range of 0.011–11 ng mL −1 with a detection limit of 0.009 ng mL −1 . The gold film was characterized by scanning electron microscopy and the results showed porous gold nanoclusters were electrochemically deposited on the glassy carbon electrode.

A general route for preparation of dye-encapsulated polymer particles via an emulsion polymerization process has been described. 1-Naphthaleneboronic acid (NBA) was encapsulated, the resultant particles were used as a fluorescence probe for cilnidipine assay based on fluorescence quenching. The sensitivity of NBA-encapsulated probe to cilnidipine was largely improved in comparison with that of free NBA. The probe showed a linear response toward cilnidipine over the concentration range of 2.0 × 10−7 to 1.1 × 10−5 mol l−1, with high sensitivity, fast response time, and good selectivity.

A novel piezoelectric immunosensor based on mixed self-assembled monolayers (mixed SAMs) formed by short-chain amine- and carboxyl-terminated thiols has been developed to immobilize antigens onto gold electrodes for detecting antisperm antibody (AsAb) in human serum samples. The properties and the enhanced performance of the affinity biosensor interface based on mixed SAMs are investigated. Most importantly, analytical results of several human serum samples using the developed technique are in satisfactory agreement with those given by the enzyme-linked immunosorbent assay (ELISA) method in the concentration ranging from 32.3 to 300.0 mU/ml. It means the procedure proposed in this paper is likely to have a great potential in research and may play an important clinical role in a few years later.

A novel biosensing interfacial design strategy has been produced by the alternate adsorption of the oppositely charged polyelectrolytes. A quartz-crystal microbalance (QCM) as a model transducer was modified by use of mercaptoacetic acid (MAA) self-assembled monolayer (SAM) and the adsorption multilayers of the oppositely charged polyelectrolytes. MAA–SAM was first applied to the gold electrode surface of the crystal, and the positively charged chitosan was used as a double-sided linker to attach the negatively charged alginate-HSA antibodies to the negatively charged MAA–SAM layer. The assembly process and conditions were studied using the real-time output device and the surface topologies of the resulting crystals were characterized by atomic force microscopy (AFM) imaging. It is discovered that the optimal pH of immobilizing antibodies was 7.2 and the suited dilution ratio of antibodies was 10:30. The proposed immunosensor in optimal conditions has a linear detection range of 12.3–184.5 μg/mL for HSA detection. Comparing with the direct immobilization method of antibodies, the immunosensor with the proposed immobilization procedure shows some advantages, such as improved sensitivity due to the well-retained antibody activity and the significantly extended detection range. In particular, the regeneration of the developed immunosensor was simple and fast. Analytical results indicate that the developed immobilization procedure is a promising alternative for the immobilization of biorecognition element on the electrode surface.

A phenol biosensor was developed based on the immobilization of tyrosinase on the surface of modified magnetic MgFe2O4 nanoparticles. The tyrosinase was first covalently immobilized to core-shell (MgFe2O4–SiO2) magnetic nanoparticles, which were modified with amino group on its surface. The resulting magnetic bio-nanoparticles were attached to the surface of carbon paste electrode (CPE) with the help of a permanent magnet. The immobilization matrix provided a good microenvironment for the retaining of the bioactivity of tyrosinase. Phenol was determined by the direct reduction of biocatalytically generated quinone species at −150 mV versus SCE. The resulting phenol biosensor could reach 95% of steady-state current within 20 s and exhibited a high sensitivity of 54.2 μA/mM, which resulted from the high tyrosinase loading of the immobilization matrix. The linear range for phenol determination was from 1 × 10−6 to 2.5 × 10−4 M with a detection limit of 6.0 × 10−7 M obtained at a signal-to-noise ratio of 3. The stability and the application of the biosensor were also evaluated.