Carbon dots (Cdots) have become a potential material for biosensing, drug delivery and bioimaging because of their excellent optical properties, high biocompatibility and low toxicity. Thus the preparation, properties and applications of Cdots have drawn great attention. In this review, Cdots were classified into two groups: grapheme nanodots and carbon nanodots, based on the difference in precursors and preparation methods. The synthetic methods of Cdots were summarized and their luminescence mechanism was analyzed. The applications of Cdots in biosensing, drug delivery and bioimaging were also discussed. The issues and challenges of Cdots were analyzed for their further development. This review summarizes the synthetic methods and luminescence mechanism of carbon dots. Their applications for biosensing, drug delivery and bioimaging are also discussed.
Laser-induced breakdown spectroscopy (LIBS), a new type of element analytical technique with the advantages such as real-time, online, non-contact and multiple elements simultaneous analysis, is a frontier analytical technique in spectral analysis. However, it is still the main problem for LIBS technique to improve the accuracy of qualitative and quantitative analysis by extracting the useful information from a large number of complex LIBS data. Chemometrics is a chemical sub-discipline of multi-interdisciplinary, which has the advantages in date processing, signal analysis and pattern recognition. It can solve some complicated problems which are difficult for traditional chemical methods. In the paper, we reviewed the research progress of chemometrics methods in LIBS from the spectral data pre-processing, qualitative and quantitative analysis in recent years. Laser induced breakdown spectroscopy(LIBS) coupled with advanced chemometrics methods has been successfully applied for the quantitative and qualitative analysis of some specific samples in various fields, and chemometrics shows a great development potential in LIBS fields.
As the main final products of the purine metabolism in human body, uric acid (UA) usually presents in serum and urine. Thus, the level of UA in biology is closely related to human health. In this work, the ultra-small CuS nanoparticles (NPs) were demonstrated to possess intrinsic peroxidase-like activity towards 3,3',5,5'-tetramethylbenzidine (TMB) substrate in the presence of H O , which yielded the blue oxidized TMB (oxTMB) with strong absorption at 653 nm. Furthermore, H O could be produced by the enzymatic reaction between UA and uricase to yield the blue oxTMB with the peroxidase mimetics activity of CuS NPs, which provided a sensitive and colorimetric method for UA detection with a linear range from 1.0 × 10 M to 1.0 × 10 M and a detection limit of 1.0 × 10 M. Moreover, the proposed method was successfully applied to the determination of UA in human serum samples, which supplied a similar result to the clinical method. In this work, the ultra-small CuS nanoparticles possess intrinsic peroxidase-like activity in the presence of H O yielded by the enzymatic reaction between UA and uricase to release ·OH free radical, resulting in the blue product of TMB. Moreover, the proposed method was successfully applied to the determination of UA in human serum samples with a simple, sensitive and selective result.
The structural change of -amylase (Ba -amylase) induced by chloride ion was studied by fluorescence spectra, Fourier-transformation infrared (FT-IR) spectroscopy and circular dichroism (CD) spectroscopy. It was found that when chloride ion concentration was below 20.0 mM, the Ba -amylase was activated by increasing chloride ion concentration; when chloride ion concentration was over 20.0 mM, the biological activity of Ba -amylase was inhibited by increasing chloride ion concentration. The spectroscopic analyses illustrated that the change in Ba -amylase biological activity was caused by the alteration in secondary structure of Ba -amylase. When chloride ion showed activation effect to Ba -amylase, part of the random coils in Ba -amylase gradually transformed to -helix and -sheet with increasing chloride ion concentration and the Ba -amylase transited from relatively disordered conformation to relatively ordered one. Whereas when chloride ion showed inhibition effect on the biological activity of Ba -amylase, part of -helix and -sheet in Ba -amylase gradually transformed to random coil with increasing chloride ion concentration and the Ba -amylase went back from the relatively ordered conformation to the relatively disordered one. This work shows the dependency of change in biological activity to alteration in secondary structure of protein molecule, which may provide some useful information in the actual application and exploration on action mechanism of proteins. The biological activities of Ba α-amylases increased quickly with the increase of chloride ion concentrations under 20.0 mM that the change was caused by transforming random coil to α-helix and β-sheet; the relative activities of Ba α-amylases decreased slowly with the increase of chloride ion concentrations exceed 20.0 mM that the change was caused by transforming α-helix and β-sheet to random coil. When chloride ion concentration was 20.0 mM, the biological activity of Ba α-amylases was the maximum.
A rapid, inexpensive and efficient sample preparation method for simultaneous extraction and determination of three pyrethroids and seven phthalate esters in samples was developed. The target analytes were extracted using a two-step extraction method including ultrasonic-assisted extraction and dispersive liquid-liquid microextraction coupled with gas chromatography-mass spectrometry (GC-MS). In ultrasonic-assisted extraction process, acetone was used as extraction solvent and extraction time was set as 3 min. In dispersive liquid-liquid microextraction process, optimized experimental conditions including 100 μL of CCl as extraction solvent and 1.0 mL of acetone as dispersant with 3% ( / ) of NaCl were adopted. The eluents were further quantitatively determined by GC-MS. All ten kinds of analytes were well separated, and the calibration curves showed good linearity, with correlation coefficients greater than 0.9992. Low detection limits of 0.0035 μg kg for DMP to 1.0 μg kg for IMIP were achieved. The method demonstrated good recoveries between the acceptable range of 79.7% for IMIP to 105.7% for TETR at three spiked levels with RSD < 8.2% for most of evaluated analytes. The method was employed for detection of samples with satisfactory results. A rapid, inexpensive and efficient sample preparation method for simultaneous extraction and determination of three pyrethroids and seven phthalate esters in samples was presented. The target analytes were extracted using a two-step extraction method including ultrasonic-assisted extraction and dispersive liquid-liquid microextraction coupled with GC-MS.
An electrochemical sensor was successfully fabricated by coupled ammoniated modification with PBS activation on glassy carbon electrodes (CA-GCE) and characterized by electrochemical impedance spectra. The CA-GCE showed outstanding electrochemical performance, and was applied to simultaneous detection of resorcinol (RC), catechol (CC) and hydroquinone (HQ), which could be ascribed to new active sites by the introduction of amino and oxygen-containing groups and H-bonds formed between hydroxyl groups of RC, CC, and HQ with amine, hydroxyl and carboxyl groups of CA-GCE. The reaction kinetics of RC, CC, and HQ and their reaction on CA-GCE were studied. Experimental results showed that the electrochemical reaction was adsorption controlled. Under the optimal conditions, the linear detection ranges for RC, CC, and HQ were 5–200 μM, 10–300 μM, and 1–300 μM, respectively, with their detection limits of 0.47, 0.23 and 0.46 μM, respectively. Interference and repeatability was further investigated. This strategy opened a new horizon for qualitative and quantitative detection of dihydroxy benzene. An electrochemical sensor for determination of the concentration of hydroquinone (HQ), catechol (CC) and resorcinol (RC) was successfully fabricated by coupled ammoniated modify with PBS activate on glassy carbon electrodes (CA-GCE). The CA-GCE showed an outstanding electrochemical behavior. The reaction kinetic of RC, CC, and HQ and their reaction on CA-GCE were studied. Finally, the method was used to determine the real water samples.
Nanopipette has emerged as a versatile nanosensor. It is desirable to expand the sensing capabilities of nanopipette by integrating multiple sensing methods into one nanopipette. In this work, we presented a seeded growth approach to facilely, cheaply and quickly deposit a gold layer with controllable length at the inner surface of the nanopipette tip. The deposited gold formed a wireless ring-shape gold nanoelectrode at the nanopipette tip and enabled multimode single entity detection. With the presence of gold at the nanopipette apex, the nanopore based resistive-pulse sensing capability was obviously improved. The integrated ring-shape gold nanoelectrode could be used as a wireless bipolar electrode for electrochemical measurement. We further demonstrated that the gold coated nanopipette could be used as a substrate for surface enhanced Raman spectroscopy. The small gold nanoparticles were introduced to speed up the gold deposition process, the whole process only needs a few minutes. The deposited gold formed a wireless ring-shape gold nanoelectrode at the nanopipette tip and enabled multimode single entity detection. In addition, the ring-shape gold at the nanopipette tip could be used as a bipolar nanoelectrode and as an effective substrate for SERS.
The positive scan polarization reverse catalytic voltammetry was used for direct detection of ascorbic acid in fruit and vegetable samples. An ascorbic acid sensor was fabricated based on Cu O nanoparticles protected by the graphene oxide (GO) layer. The common copper electrode was first electrooxidized in strong alkaline solution to generate Cu O nanoparticles on the electrode surface, then GO was electrodeposited to form a protective layer covered on the surface of Cu O nanoparticles. The resulting sensor exhibited excellent electrocatalytic activity toward oxidation of ascorbic acid. There was a wide linear range between the difference value peak current of the sensor and the ascorbic acid concentration from 1.25 × 10 M to 1.60 × 10 M, with a detection limit of 5.90 × 10 M ( / = 3). The results demonstrated that the proposed method possessed excellent detection capability, including fast response, high reproducibility and stability. An excellent ascorbic acid (AA) sensor was prepared based on the Cu O nanoparticles protected by graphene oxide layer. The positive scan polarization reverse catalytic voltammetry (PSPRCV) was employed for direct detection of AA in fresh fruits and vegetables.
Genistein is an important isoflavone that has been widely used to prevent blood disease and cancer. In this work, a novel genistein electrochemical sensor was developed based on the composite of molecularly imprinted polymer (MIP) and carboxylated multiwalled carbon nanotubes (cMWCNTs). The MIP layer was electropolymerizated on the cMWCNTs modified electrode using carbazole as functional monomer and genistein as template molecule. The morphology and electrochemical performance of MIP/cMWCNTs were characterized by scanning electron microscopy (SEM) and cyclic voltammetry (CV), respectively. A series of experimental conditions were optimized, including the pH value of supporting electrolyte, electropolymerization potential range, molar ratio of functional monomers to template molecules, numbers of cycle, accumulation potential and accumulation time. Under the optimal conditions, the resulting electrochemical sensor (MIP/cMWCNTs/GCE) showed high performance, such as high sensitivity and selectivity towards genistein, a wide linear range (0.02–7.00 μM) and a low limit detection of 0.006 μM ( / = 3). The electrochemical sensor was applied to determination of genistein in tablets and human urine samples with satisfactory recoveries (97.9%–102.8%), and the accuracy of the sensor was demonstrated with the HPLC method. A new molecularly imprinted electrochemical sensor for genistein detection was prepared by fabricating the MIP layer on the cMWCNTs modified electrode using carbazole as functional monomer and genistein as template molecule. The electrochemical sensor (MIP/cMWCNTs/GCE) showed high performance towards genistein detection, and was successfully applied as a simple and efficient tool in tablets and human urine samples.
A simple and effective method for modulating nanoparticles (NPs) translocation through nanopore by tuning the surface change of chemically modified gold coated nanopore was developed. The gold-coated pore is simply prepared from a nanopipette and the partially insulated gold coating can be utilized to effectively concentrate NPs near the nanopore entrance. The surface modification of gold near the orifice effectively modulates the NP translocation behavior, mainly through electrostatic force and chemical interactions. This system can be extended to the detection of biological entities, such as virus and exosomes which have similar size of NPs. After wax insulation, the gold coated nanopipette demonstrates nice electrochemical properties of nanoelectrode. The surface modification of gold near the orifice effectively modulates the NP translocation behavior, manly through electrostatic force and chemical interactions. In the next step, this method can be applied to protein, DNA, and other single molecules.
The novel methods for rapid detection and discrimination of aroma have gained huge attentions not only because of the growing demands for food safety supervision, but also due to their high potentials in monitoring and regulating fermentation process in food production. In this work, a prototype of electronic nose was developed by eight metal oxide semiconductor gas sensors which were fabricated based on two different types of CuO heterojunction, namely ZnO-CuO (n-p) and NiO-CuO (p-p). The sensing performance of as-fabricated electronic nose towards 7 volatile organic compounds (VOCs) gases samples and 4 real samples of Chinese Jing Wine was conducted. The responses were analyzed with standard statistical methods, e.g., hierarchical clustering analysis (HCA), and were distinguished accurately against one another with no errors or misclassifications. In this work, based on two different types of copper oxide heterojunctions, ZnO-CuO and NiO-CuO, an electronic nose was developed. The sensing properties of self-made electronic nose and four years of real wine samples were studied. The results were analyzed by hierarchical clustering analysis (HCA). Accurate identification of samples was achieved.
Cu-Co Prussian Blue analogue (Cu [Co (CN) ] )/multi-walled carbon nanotubes (Cu-Co PBA/MWCNTs) composite was synthesized for fabrication of an electrochemical sensor for detection of nitrite. The morphology and composition of the fabricated nanomaterial were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to investigate the electrochemical behavior and mechanism of the fabricated biosensor. Experimental results showed that Cu-Co PBA/MWCNTs/GCE had excellent electrochemical activity towards nitrite, which was superior to that of Cu-Co PBA and MWCNTs. Under the optimal conditions, a wide linear range from 10–400 μM and 400–2100 μM and a detection limit of 0.5 μM were obtained. Moreover, this sensor was employed to determine the concentration of nitrite in ham sausage and mustard samples, and showed excellent selectivity, good anti-interference, repeatability and satisfied recovery.
A fluorescent probe based on isorhamnetin (Iso)-cyclodextrin (CD) inclusion for detecting Cu2+ was synthesized. A major fluorescence emission peak at 542 nm was observed for isorhamnetin (Iso) in buffer solution (pH 7.40) when the excitation wavelength was 390 nm. It was surprisingly found that (2-hydroxypropyl)-beta-cyclodextrin (beta-CD) could enhance the fluorescence intensity of Iso, and the major fluorescence peak was shifted to 557 nm. UV-vis spectrum showed that the Iso-beta-CD system was formed by hydrogen bond and hydrophobic interaction. And the fluorescence intensity of Iso-beta-CD system was stronger and more stable compared with Iso. Further study indicated that Iso-beta-CD system had good selectivity and sensitivity toward Cu2+. When Cu2+ was added, the fluorescent emission intensity of Iso-beta-CD system was quenched, while other metal ions could not bring about obvious change, which meant that the Iso-beta-CD system had good selectivity toward Cu2+. The fluorescence titration spectra indicated that the concentration of Cu2+ was inversely proportional to fluorescence intensity, and fluorescence emission intensity was linearly correlated with the concentration of Cu2+ in the range of 0.05-6.0 mu M. The calibration equation was y = -11.66x + 781.13 (R-2 = 0.996), with a limit of detection of 0.017 mu M (S/N = 3). The possible reaction mechanism was studied by UV-vis spectroscopy and Job's plot method. The results indicated that Cu2+ could combine with Iso-beta-CD system. The stoichiometric ratio for the complex of Iso and Cu2+ was 2: 1. The formation of Iso-beta-CD-Cu(II) complex led to the extension of the conjugated system and the intramolecular charge transfer (ICT) took place. Therefore, fluorescence of Iso-beta-CD system was quenched. At last, the probe was successfully applied to determination of Cu2+ in water samples, vegetables and fruits with good recoveries, and the results coincided with those obtained by ICP-AES or AAS methods.
A large area graphene platform electrode (GPE) was fabricated by transferring chemical vapor deposition (CVD) grown graphene on Cu foils onto polyethylene terephthalate (PET) substrates with the aid of polymethyl methacrylate (PMMA). Cobalt hexacyanoferrate (CoHCF) was electrodeposited on GPE by cyclic voltammetry. The morphology and electrochemical properties of CoHCF/GPE were studied by scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS) and the electrochemical measurements. The CoHCF/GPE showed favorable sensing effect toward H O . A novel non-enzyme H O sensor was constructed. Under the optimal experimental conditions, the proposed sensor responded to the addition of H O very quickly (about 2 s) with a wide linear rang (0.005–1.2 mM) and a low detection limit (7.1 nM). This sensor was easy to be fabricated and showed excellent stability and anti-interference ability. A large area graphene platform electrode (GPE) was fabricated by transferring chemical vapor deposition grown graphene on Cu foils was transferred to polyethylene terephthalate (PET) substrates with the aid of polymethyl-methacrylate. Cobalt hexacyanoferrate (CoHCF) was electrodeposited on GPE by cyclic voltammetry. The CoHCF/GPE showed favorable sensing effect toward H O .
A specific polyclonal antibody was prepared based on a new hapten with stable structure. Based on this, an indirect competitive enzyme-linked immunosorbent assay (icELISA) was established for determination of tylosin residues in food and environmental samples. The experimental conditions were optimized as follows: the coating antigen and antibody were respectively diluted by 6000 times and 2000 times, and the competitive reaction time was 40 min. Under the optimized conditions, the method showed a detection limit of 0.07 ng mL , an IC of 1.39 ng mL and a linear range of 0.17–11.0 ng mL . The recoveries of spiked raw milk and water samples were ranged from 78.4% to 105.6%, with the RSDs of less than 15%. Good correlation between icELISA and HPLC method was obtained for spiked samples ( = 0.97). This method was suitable for the determination of tylosin residues in milk and water samples. A hapten with simple and stable structure was synthesized based on tylosin, and specific polyclonal antibodies were obtained through animal immunity experiments. Based on this antibody, an indirect competitive enzyme-linked immunosorbent assay ( ELISA) for the detection of tylosin residues in pure milk and water samples was established. This method was sensitive and stable, providing an effective reference for the immunoassay of these substances in practical applications.
Capillary electrophoresis based systematic evolution of ligands via exponential enrichment (CE-SELEX) was reported as a homogeneous efficient method for high-affinity selection of aptamer, with several merits involving screening in free solution without nonspecific binding, capable of high-efficient separation, low-sample consumption, and saving money. There are few studies regarding the aptamer selection against small molecule using CE-SELEX, resulting from the aspects of less binding sites and the negligible variety of its complex with nucleic acid in the electrophoretic mobility. In this study, we performed the aptamer selection towards a small molecule target of clenbuterol hydrochloride (Clen) by CE-SELEX. In brief, Clen were first incubated with an 80 nt ssDNA library, and CZE-UV approach was used to separate complex and random ssDNA. The complex was then collected into a vial followed by PCR amplification. Through three round selections, the third library was selected to clone and ten sequences were finally obtained. The dissociation constant (K ) of three potential candidates (Apt 4, Apt 7 and Apt 12) were determined by CE-LIF, and showed high affinities of 9.315 × 10 M, 1.040 × 10 M and 1.143 × 10 M, respectively. The result of m-Fold software analysis showed that the above three sequences could form stem-loop structure, and the Apt 4 gave the lowest free energy and the most stable structure. Using salbutamol as a control, three selected aptamers were verified with high specificity.
The polygonal electrode linear ion trap (PeLIT) can produce quadrupolar electric field plus some higher order field, which balances the relationship between mass resolution and electrode manufacturing difficulties. The electrodes of PeLIT are relatively simple, but have a good mass resolving power. This study investigated the relationship between the electric field distribution and the ion trap structures, and the performances of PeLIT through theoretical simulation and experimental study. Research results of simulation showed that the polygonal electrode linear ion traps with different structures had different electric field distributions and mass analysis performances. The negative decapole field distorted the performances significantly. The experimental results showed that the mass resolution of reserpine ions ( / 609) was more than 2500 using a polygonal electrode ion trap. At the same time, mass selective excitation and tandem mass spectrometry experiments were also carried. A linear ion trap was built with four polygonal electrodes which could produce quadrupolar electric field plus some higher order fields. The experimental results showed that its mass resolution was more than 2500, and the mass selective excitation and tandem mass spectrometry performance were also very well.
Microfluidics has been widely used in the life science, analytical chemistry, environmental science and other fields in the recent years. Traditional microfluidics systems usually use a highly integrated system with multiple components for handling the fluid in the micro/nano scale. The design and fabrication of integrated microfluidics usually require highly sophisticated instruments and operation professionals. With the experience inherited from integrated circuit and micro electro mechanical system, the modular microfluidics system has been experienced a rapid development in recent years. Modular microfluidics system is a combination of a series of individual modules to achieve complicated liquid handling functions. Compared with conventional microfluidics approach, the modular microfluidics method has the potential in significantly reducing the fabrication cost by using the massive production of single chip, besides, it is easy to be operated, and the user can easily assembly the modules to obtain their customized microfluidics system. The concept of modular microfluidics also indicates the future development path for the standardization of microfluidics system and also provides a promising approach for the industrial massive production of microfluidics. However, the study of modular microfluidics is still in an early stage. Although lots of studies have been conducted with varies materials, fabrication methods and interface technologies, issues like modular interface still restricted the further development of microfluidics. In this paper, a comprehensive review for the latest research on the modular microfluidics and applications in biological and medical fields is provided, and the future research trends of modular microfluidics is also discussed. Modular microfluidics system is a combination of a series of individual liquid handling modules. Compared with conventional microfluidic protocols, with modular microfluidics, user could easily combine the modules for their own customized microfluidic system, and each module can be fabricated massively to significantly reduce the fabrication cost. In addition, the concept of modular microfluidics also shows a way for the future standardization of microfluidics.
Fluorescent carbon quantum dots (CQDs) were synthesized by one-step hydrothermal treatment with apple juice as raw material. The result indicated that the fluorescence could be quenched by Hg with high specificity. Based on this phenomenon, a selective and sensitive sensor was constructed for the detection of Hg in phosphate solutions (pH 7.0). The fluorescence intensity showed linear responses with Hg concentration ranging from 5.0 to 100.0 nM and 1.0 to 50.0 μM, with the detection limit of 2.3 nM ( / = 3). The as-fabricated sensor was further extended for the determination of Hg in real water samples. Fluorescent CQDs were synthesized with apple juice under hydrothermal conditions, which exhibited clear yellow in visible light but a bright blue fluorescence under UV light. CQDs displayed an excitation dependent emission, accompanied by the decrease of the fluorescence intensity.
A method for analysis of short-chain chlorinated paraffins (SCCPs) in water based on solid-phase extraction (SPE) was established using electron capture negative chemical ionization mass spectrometry (GC-ENCI-MS). The SPE parameters, including the sorbent, eluent and elution volume were optimized. The Agilent Bond Elut-C was precleaned with 3 mL of hexane and 3 mL of methanol, and subsequently conditioned with 3 mL H O prior to use. After the water samples were enriched by the cartridge, the sample was washed with 3 mL of 10% ( ) methanol and eluted with 3 mL of hexane-dichloromethane (1:1, ) solution. The results indicated that the limits of detection (LOD) for SCCPs were 18 ng L , while the corresponding limits of quantitation (LOQ) were 60 ng L . The spiked recovery range was 90%–135%, with a relative standard deviation of less than 10%. Finally, 20 surficial water samples around Beijing were collected and SCCPs contents were analyzed using the proposed method. The SCCPs concentrations ranged from less than LOD to 682 ng L with a mean concentration of 216 ng L . A detection method for short-chain chlorinated paraffins (SCCPs) in water samples was established. SPE parameters including sorbent, eluent and elution volume were optimized. The results showed that the optimised procedure can be successfully applied to the analysis of SCCPs in water samples.