MicroRNA (miRNA) is a promising new type of biomarkers but at a low fM level and hard to be analyzed. Herein proposed is an innovated surface plasmon resonance imaging (SPRi) method merged with a novel in-plane and vertical signal amplification strategy, that is, orthogonal signal amplification to enable a direct determination of sub-fM miRNA-15a (a multiple tumor diagnostic biomarker). The core idea is to add more mass on a target sample spot first along the surficial direction, then upward from the surface. In detection of miRNA, this was realized by coupling a miRNA-initiated surficial cyclic DNA–DNA hybridization reaction with a DNA-initiated upward cyclic polymerization reaction. A perfect SPRi sensing chip with isolated gold islands bordered by hydrophobic CYTOP was fabricated and used to obtain high-quality chip with low fabrication difficulty. As a result, SPRi contrast largely increases, able to reach a limit of detection and limit of quantification down to 0.56 and 5fM for miRNA-15a, about 107-fold improvement of sensitivity compared with a common SPRi detection. The method could quantify standard miRNA-15a spiked in human serum with an ideal recovery ranging from 98.6% to 104.9% and was validated to be applicable to the direct determination of miRNA-15a in healthy and cancer human serums. The orderly and controllable in situ sensitizing strategy is powerful and readily extendable to detection of other miRNAs.

•The advances on improving the detection sensitivity of SPRi were summarized after analysis of 89 papers since 2005.•The focus is on non-instrumental measures, especially on chemistry-based signal amplification.•Instrumental measures are also summarized based on our opinion.Surface plasmon resonance imaging (SPRi) has more and more applications in the fields of biology and life sciences due to its unique features of label-free and high-throughput detection and workability in physiological conditions, however it is suffering from insufficient sensitivity, especially in detecting the small molecules or low level of substances. Various methods have since been developed to improve its sensitivity, but it lacks of summary except for their working principles, setups and applications. This review is thus designed to summary the sensitivity-oriented research progresses, covering signal enhancement and/or amplification, and noise and background suppression, with chemistry-enhancing strategies as focus and non-chemistry as supplement. A brief prospect in near future is also given.

A stepwise strategy was proposed to controllably amplify surface plasmon resonance imaging (SPRi) signals and used to establish a method for sensitive detection of small saccharides and large glycoconjugates. The key is to enlarge the target analytes step by step through a cyclic recognition reaction of concanavalin A (ConA) with dextran, which can easily be integrated into SPRi detection. The reaction is theoretically expected to proceed with infinite cycles by addition of ConA and dextran one after another, and in practice, it allows for performing signal amplification for up to 20 steps, which nearly reaches the limit of the propagation depth of surface plasmon waves. Because of the nonspecific adsorption effect, the maximum signals of small sugars were measured at steps 5–7 by the use of small molecules like ethanol amine to block the nonspecific adsorption. The real applicability of the method was validated by SPRi determination of either immobilized saccharides and glycoproteins or captured carcinoembryonic antigen (CEA) from patient samples with a limit of detection down to 2.5 μM glucose or 50 pg/mL of CEA. A wide extendibility of the method was confirmed by detecting other ConA-recognizable analytes like human IgG, ovalbumin, α-fetoprotein, and analytes convertible to ConA- or dextran-recognizable forms. Notably, other cyclic reactions specific to saccharides or other analytes are in theory exploitable, which will further widen the applicability of the method and strategy.

It is broadly interesting but remains a big challenge to explore nanomaterials-based methods to enable naked-eye observation and determination of ultratrace biomarkers and drugs. In this study, we developed a straightforward and extendable plasmonic nanosensor to enable visually quantitative determination of ultratrace target molecules through combining the use of enzyme-mimetic gold nanoclusters (AuNCs). Starting from sandwiched antibody–antigen (i.e., an analyte)-antibody structure, we conjugated AuNCs on the outer layer antibody to catalyze the decomposition of hydrogen peroxide used to reduce HAuCl4 into gold nanopartilces (AuNPs) for naked eye readout. This strategy is in theory applicable to all immunoreactions available and the protocol proposed to attach AuNCs onto an antibody is suitable to all proteins. The applicability of this type of nanosensor was validated by the determination of various ultratrace analytes such as protein avidin, breast cancer antigen, thyroid hormone, and even methamphetamine (MA), giving a naked-eye-readout limit of detection (LOD), down to 1.0 × 10–20 M protein avidin, 7.52 × 10–14 U/mL breast cancer antigen 15–3, 2.0 × 10–15 mg/mL 3,5,3′-L-triiodothyronine and 2.3 × 10–18 mg/mL MA. This strategy is thus considered an ultrasensitive way to fabricate plasmonic nanosensors, having wide and invaluable application potential in clinical, biological, and environmental studies, and in food quality control.

The DNA-targeting platinum complex cisplatin is one of the most successful drugs for clinical treatment of solid tumors, and several new analogues of transplatin have shown cytostatic activity recently. The specific recognition of platinated DNA with cellular proteins is of great interest for better understanding of the pharmaceutical mechanisms. Herein, a surface plasmon resonance imaging (SPRi) method to differentiate the interaction between the protein human high mobility group box 1 (HMGB1) and DNAs, and human nuclear protein positive cofactor 4 (PC4) and DNAs has been developed. Four kinds of DNAs were immobilized on the gold films including platinated-DNA adducts (cisplatin and trans-[PtCl2(NH3)(thiazole)] (trans-PtTz) damaged DNAs; referred to as cisPt–DNA1 and transPtTz–DNA2, respectively) and native DNAs (DNA1 and DNA2, as controls). The validation of the method has been proven by the specific recognition of HMGB1 and cisPt–DNA1 first. The results obtained indicated that the PC4 was more likely to bind to platinated DNAs (cisPt–DNA1 and transPtTz–DNA2) than the native DNAs. Temperature-dependent kinetics and thermodynamics revealed that the recognition behavior was not affected by a temperature changefrom 15 °C to 42 °C. This label-free method provides authentic results, as the controls can be simultaneously determined by a single chip under the same conditions, and this makes it suited for other high throughput analyses of interactions between drug-damaged DNAs and proteins to better understand the activity/inactivity mechanisms of drugs and drug screening/discovery.

•Glutaraldehyde-cross-linked chitosan of different states (solution, gel, nanoparticle, etc.) with luminesce at ca. 670 nm were prepared for the first time.•They are quite inert and anti-photobleaching.•Their nanoparticles (5.6 nm) could image the nucleoli of living HeLa cells with low cytotoxicity.Biocompatible glutaraldehyde-cross-linked chitosan with new red fluorescence were prepared for the first time and were shaped into nanoparticles via inverse-microemulsion method. They could luminesce at ca. 670 nm either as powders and nanoparticles or in real and gelling solutions or suspensions, having a lifetime of 1.353 ns and a quantum yield of 0.08 in solution or 0.01 in solid state. The new-formed pyridinium structures and the intramolecular charge transfer effect are considered to be responsible for the new red emission, which have been proved by FTIR, 13C NMR, and some calculation using Gaussian 09, respectively. Strikingly, they are quite inert and anti-photobleaching, with only <3% loss of fluorescent intensity per minute in average under a continuous laser illumination at 633 nm and 50 μW. Especially, their nanoparticles (5.6 nm) could enter into the negative nucleoli of living HeLa cells with low cytotoxicity for high contrast imaging inspections.

•A method was developed for preparing a graphene-coated SPME fiber in <25 s.•The fabricated fibers are very stable, sustainable to 300 °C and long term of storage.•With mossy surfaces the fibers possess high extraction capacity.•They could analyze trace polycyclic aromatic hydrocarbons in beverages.Graphene's unsurpassed specific surface area (up to 2630 m2/g) makes it be an ideal absorbent. To promote its use as a sorption coating in solid phase microextraction, an ultrafast method was established, able to coat a stable layer of graphene on a metal fiber in only 23 s, with adjustable coating thickness between 10 and 40 µm by using sleeve barrels. The core idea includes: (1) use of semi-polymerized dimethylsiloxane as a sticky pre-liner to glue graphene and (2) rapid conversion from pre-liner to elastic polydimethylsiloxane (PDMS) to fix the glued graphene. Ultrafast conversion of the pre-liner to PDMS was achieved by direct heating of the metallic fibers. The method produced very stable and durable fibers, capable of being used for at least 120 extractions–desorption cycles and stored at room temperature for at least 20 months. Interestingly, the new method could always coat a layer of mossy graphene on the fibers to largely increase their extraction capacity. Their limit of detection reached 2 pg/L PAHs, being about 3 orders of magnitude better than that of the reported graphene-based fibers. They were applicable to the direct extraction of trace PAHs in beverages, with a linear regression range from 10 to 1000 pg/L, and recoveries of 88.9–105.3%. The relative standard deviations of peak area were 2.9–8.9% for the same fiber and 3.0–10.0% for different fibers. The method is also suitable for re-coating a used fiber and extendable to fast coating other solid sorbents on heat-resistant supports.

Packing of stable and crack-free photonic crystals (PCs) into micro channels is a prerequisite for ideal separation, but often takes several days and many steps, including assembly and immobilization. This work was dedicated to finding a fast, one-step solution. Simply by heating and blowing away the vapor, the packing of silica PCs into micro channels by classic evaporation-induced assembly was greatly accelerated and could unite the immobilization into one step. An apt method was thus established, which was able to pack 2 cm PCs into microfluidic channels in 15 min, saving a lot of time. The packed PCs showed no evident cracks along the borders of their continuous domain, therefore they are capable of withstanding an anti-electrical field at 2000 V cm−1 for 5 h and storage in water for 2 months. This enables ultra-fast separation of amino acids along a 2.5 mm PC in 4 s, and peptides along a 10 mm PC in 12 s. The separation was highly efficient and reproducible, with a 300 nm plate height and 0.24%–0.35% relative standard deviation of migration time. This one-step approach is extendable to other gelling particles, and the resulted stable, crack-free PCs would have large potential in ultra-fast separation of other analytes.

Accurate determination of copper in complex biological media such as cells is quite difficult, and an analytical strategy based on copper-modulated formation of core–shell gold nanorods is described. Selective and label-free sensing can be achieved by measuring the change in the localized surface plasmon resonance absorption. The technique can determine trace amounts of copper in human serum, urine, and red blood cells without or with minimal sample pretreatment. The Cu detection limits are 20.67 μM in human serum, 0.193 μM in human urine, and 3.09 × 10–16 g in a single cell. The advantages of the technique are the high selectivity, simple or no sample pretreatment, and label free. Boasting a practical detection limit down to 2 fM, only 103 red blood cells are needed to conduct the analysis and the technique may be extended to the detection of trace amounts of copper in a single cell.

Interaction of straight chain alcohol vapors with MOF-199-functionalized films was studied by SPR. The signals had linear relationships with the concentration of alcohols over a wide range from 0 to 70% (v/v) and were reversible in proportional to the chain length, with R2 all above 0.99.Relationship of SPR signals with the chain length of alcohols on OH- (A) and COOH- (B) MOF-199 films and on bare gold film (C). The data were averaged over 10 cycles of adsorption and desorption.

A one-step photochemical approach was established to quickly and specifically synthesize uniformly dispersed silver nanoparticles (AgNPs) on reduced graphene oxide (rGO) nanosheets. Silver–ammonia and graphene oxide (GO) were used as precursors to enhance the coordination-based adsorption of silver cations onto the negatively charged GO surface through ligation with ammonia, which could also continuously stabilize the nucleation and growth of AgNPs. The method allowed the easy control of the coverage percentage of AgNPs on rGO in a range from 7.2% to 81.6%. The prepared AgNPs-rGO composites were highly dispersible and stable in water in the absence of any stabilizing agent, and showed excellent catalytic properties in the reduction of 2-nitroaniline to 1,2-benzenediamine.

An easy chemical strategy was proposed and used to establish a method for direct anchoring of intact saccharides on solid surfaces with well conserved bioaffinity. The anchoring was achieved by temperature-modulated stepwise reactions with cyanuric chloride as a key linker, and was successfully applied to the fabrication of saccharide chips. To demonstrate, 15 intact reducing and nonreducing saccharides with various molecular sizes were dotted on a cyanuric-chloride-modified chip (1.0 × 1.0 cm2) and made to react with lectins. As expected, the anchored saccharides were capable of recognizing their target lectins, and more exciting were the perfect conservation of the specific recognizing ability of the anchored monosaccharides such as mannose, glucose, and even fructose (interacting only weakly with concanavalin A). This conservation was ascribed to the maintenance of the original structure (especially the anomeric configuration) of saccharides after immobilization and to the allowance of the anchored saccharides to rotate with and/or on the scaffold of cyanuric chloride, which makes them easily adapt to the recognition-preferred spatial position. The expected linkage of saccharides on cyanuric chloride and the maintenance of their anomeric configuration were characterized by mass spectrometry and nuclear magnetic resonance, respectively. The new method can be highlighted not only by its conservation of saccharide bioaffinity and universal applicability but also by its merits of easy manipulation or facile control of the reactions and cost-effectiveness due to the use of extremely cheap cyanuric chloride.

A new strategy was explored for the visual determination of Cu2+ using copper-catalysed in situ formation of Ag nanoparticles. In this method, only common reagents were used and the pre-synthesis and modification of nanoparticles are avoided. Ag+ can form a milk-white suspension (AgBr) with Br− in an aqueous solution composed of AgNO3, cetyltrimethylammonium bromide, ascorbic acid, bovine serum albumin, and NaNO3. The reaction will be stopped by addition of Cu2+, accompanied by a colour change from milk-white to orange or brilliant yellow. Cu+ (the reduction product of Cu2+) consumes the dissolved O2 and prevents the O2 from oxidizing the newly reduced Ag atoms (by ascorbic acid) back to Ag+, facilitating the further aggregation of Ag atoms to become Ag nanoparticles. The visible colour change was shown to be specific towards Cu2+ over most other metal ions. The limit of detection was 0.75 μM Cu2+ by the naked eye and 0.25 μM by spectrometer. Quantitation of Cu2+ was achieved in a linear range from 0.25 to 2.0 μM. This method was validated by measuring real water and serum samples, giving results agreeing well with the data reported and measured by inductively coupled plasma mass spectrometry. The recovery was 95.6–106% for untreated tap water and 96.0–100% for resin-pre-treated water and serum samples.

A surface plasmon resonance (SPR) method was presented to discriminate hemodialyzed T-lymphocytes from the normal based on antibody–cell recognition. By dynamic reaction with fixed anti-human CD4 antibody, SPR could offer significant signals to distinguish hemodialyzed patients from the healthy controls within 200 s after the cell injection in respect of either rising speed or maximum binding capacity (p < 0.01). The ratio method is also used to exclude the non-specific adsorption. The percentage of hemodialyzed patients’ CD4+ T cells against the healthy control is 69 ± 18%. The most attractive of the present method is its ability to detect the intact and label-free lymphocytes, and further to detect the subpopulations, or proteins secreted by the desired lymphocytes subset.

A method was proposed to improve the quality of noise- and/or uneven background-degraded images obtained by surface plasmon resonance imaging experiments. The noise was suppressed by adaptive median filter in combination with wavelet transform, while the uneven background was flattened by subtraction with a three-dimensionally fitted surface. These operations improved the signal-to-noise ratio from 23.83 dB to 41.36 dB for real images and widened the quantitative linear range of picture gray value vs. concentration for about one order of magnitude, with linear correlation coefficient increased from 0.9558 to 0.9982. The method can be performed repeatedly until a better result is obtained and is thus cost-effective, highly competitive to experimental strategies and other computational methods.Highlights► We present a method to improve the quality of noise- and uneven-background SPR image. ► The noise was suppressed by adaptive median filter and wavelet transform. ► The uneven background was flattened by subtraction with a fitted surface. ► This method can largely improve the performance of quantification.

A universal photochemical method has been established for the immobilization of intact carbohydrates and their analogues, and for the fabrication of carbohydrate microarrays. The method features the use of perfluorophenyl azide (PFPA)-modified substrates and the photochemical reaction of surface azido groups with printed carbohydrates. Various aldoses, ketoses, nonreducing sugars such as alditols, and their derivatives can be directly arrayed on the PFPA-modified chips. The lectin-recognition ability of arrayed mannose, glucose, and their oligo- and polysaccharides were confirmed using surface plasmon resonance imaging and laser-induced fluorescence imaging.

An enhanced sensitive biosensor has been developed to detect biological targets by tailoring the localized surface plasmon resonance property of core–shell gold nanorods. In this new concept, a shell layer is produced on gold nanorods by generating a layer of chalcogenide on the gold nanorod surface after attachment of the recognition reagent, namely, goat IgG and antigen of schistosomiasis japonica. The bioactivity of these attached biomolecules is retained and the sensitivity of this biosensor is thus enhanced significantly. The plasmonic properties of the gold nanorods attached with the biomolecules can be adjusted and the plasmon resonance wavelength can be red-shifted up to several hundred nanometers in the visible or near infrared (NIR) region, which is extremely important to biosensing applications. This leads to a lager red-shift in the localized surface plasmon resonance absorption compared to the original gold nanorod-based sensor and hence offers greatly enhanced sensitivity in the detection of schistosomiasis japonica. The human serum infected with schistosomiasis japonica diluted to 1:50,000 (volume ratio, serum/buffer solution) can be detected readily. The technique offers enhanced sensitivity and can be easily extended to other sensing applications based on not only immuno-recognition but also other types of specific reactions.

A fast, simple and cost-effective one-pot labeling strategy coupled with capillary zone electrophoresis was developed for the complete separation of amino acid mixture. The strategy includes two steps of reactions: Cyanuric chloride was made to react first with 7-amino-1,3-naphthalenedisulfonic acid monopotassium salt at 0 °C for 10 min, and then with amino acids at 55 °C for 6 min. The resulted products, after diluted with water, were injected into capillary zone electrophoresis system for separation. Using a running buffer of 20 mM sodium tetraborate decahydrate at pH 10.1, nineteen amino acids were efficiently separated in 25 min, with relative standard deviation of 0.36–1.6% and 0.96–2.1% (within and between days, respectively) for migration time and 0.030–1.6% and 0.22–2.4% (within and between days, respectively) for peak area. The proposed method has been successfully applied to the determination of free amino acids in biofluids, including human serum, urine, and saliva. The linearity of quantification was over two orders of magnitude for most amino acids, with a correlation coefficient larger than 0.999. The average recovery, determined by spiking a known amount of amino acid standards into real samples, was in a range from 91.6% to 105.9%. This method can be a noninvasive means since it could directly assay the urine and saliva samples.Graphical abstract.Highlights► One-pot labeling for amino acid analysis. ► Simplified derivatization procedure with cost-effective reagents. ► Speed of reaction at mild conditions. ► Efficient separation of nineteen amino acids using capillary zone electrophoresis without any additive. ► Successful analysis of human serum, saliva and urine.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) does not work efficiently on small molecules (usually with molecular weight below 500 Da) because of the interference of matrix-related peaks in low m/z region. The previous methods developed for this problem focused on reducing the peaks caused by the traditional matrices. Here, we report a novel strategy to analyze small molecules in a high and interference-free mass range by using metal-phthalocyanines (MPcs) as matrices which should be capable of forming matrix-analyte adducts. The mass of the target analyte was calculated by subtracting the mass of MPc from the mass of the MPc–analyte adduct. MPcs were also detectable and could serve as internal standards. Various MPcs with aromatic or aliphatic groups and different metal centers were then synthesized and explored. Aluminum-phthalocyanines (AlPcs), gallium-phthalocyanines (GaPcs), and indium-phthalocyanines (InPcs) were efficient matrices to form MPc–analyte adducts in either the positive or negative ion mode. The detection limits varied from 17 to 75 fmol, depending on analyte types. The mechanism of adducts formation was also proposed. Collectively, our strategy provides a novel and efficient way to analyze small molecules by MALDI-TOF MS.Using metal-phthalocyanines (MPcs) as matrices, small molecules were detected in the form of MPc–analyte adduct in a higher mass region by MALDI-TOF MS.Figure optionsDownload full-size imageDownload high-quality image (52 K)Download as PowerPoint slide

In this article, the Poincare-Lighthill-Kuo (PLK) method is used to derive an analytical expression on the stability boundary and the ion trajectory. A multipole superposition model mainly including octopole component is adopted to represent the inhomogeneities of the field. In this method, both the motional displacement and secular frequency of ions have been expanded to asymptotic series by the scale of nonlinear term ε, which represents a weak octopole field. By solving the zero and first-order approximate equations, it is found that a frequency shift exists between the ideal and nonlinear conditions. The motional frequency of ions in nonlinear ion trap depends on not only Mathieu parameters, a and q, but also the percentage of the nonlinear field and the initial amplitude of ions. In the same trap, ions have the same mass-to-charge ratio (m/z) but they have different initial amplitudes or velocities. Consequently, they will be ejected at different time through after a mass-selective instability scan. The influences on the mass resolution in quadrupole ion trap, which is coupled with positive or negative octopole fields, have been discussed respectively.

A capillary electrophoretic method was explored to assay aromatic amines in food samples. With an inline-coupled transient isotachophoretic stacking approach, the method has yielded about 200-fold improvement of sensitivity in UV detection of three primary aromatic amines and melamine. By using K+ as a leading ion and Tris+ as a terminating ion, a plug of 10 cm (equivalent to 0.44 μL) sample solution was allowed to introduce into a 60 cm (50 cm effective) capillary for separation, giving limits of detection down to 2.0 × 10−8 M. Baseline separation was achieved within 10 min, with relative standard deviation of 0.41–0.75% (intra-day) or 1.2–1.5% (inter-day) for migration time and 3.8–4.3% (intra-day) or 5.2–6.7% (inter-day) for peak area. The method was directly applicable to assaying the melamine in powder milk samples, with recovery in between 92.0% and 107.1%. The method could also be applied to the analysis of trace primary aromatic amines migrating from composite food packaging bags after combination of a 10-fold off-line concentration step, with limit of detection down to less than 1 μg/L. By this method, 4,4′-diaminophenylmethane and 2,4-diaminotoluene were thus found in three types of composite food packaging bags.

In this research, two new types of optical biosensors were explored from Au2S-coated gold nanorods (Au2S-coated GNRs) chemically attached with human IgG as recognizing probes. The first type of biosensors were suspended GNRs and exhibited sensitive shift of longitudinal plasmon wavelength in response to anti-human IgG, with the limit of detection down to 67 pM. The second type of sensors were on-chip-immobilized GNRs, able to be used repeatedly through measuring the change of plasmon absorption intensity at a fixed wavelength, with the limit of detection down to 33 pM. The latter sensors suited for dynamic measurements, having linear response over rang from 33 pM to 1.35 nM. Both the types of sensors not only preserved the desirable features of common GNR sensors but also easy for preparation and manipulation. The concept and methodology suggested in this study can serve as the basis to develop new methods for molecular binding events or other applications like in medical researches.

A surface plasmon resonance imaging method has been developed for high throughput recognition and determination of low level glycoproteins with limited sample volume at least down to 50 nL. Chicken ovalbumin and immunoglobulin G were chosen as model compounds while bovine serum albumin and lysozyme were used as control. Each protein, at a concentration of 0.0080–1.0 mg mL−1, was printed on one gold sensing film, and the films were simultaneously reacted with a probe solution and viewed using a laboratory-built surface plasmon resonance imaging system. The imaging signals were dependent on the concentration and the type of analyte, with a limit of detection down to at least 0.5 ng. The glycoproteins dotted at either 1.0 mg mL−1 or 0.010 mg mL−1 were easily differentiated from the non-glycoproteins by reaction with 200 nM concanavalin A (con A), giving a limit of recognition down also to 0.5 ng glycoprotein. This imaging method was hence considered a new tool for analyzing glycoproteins.

A panorama of sample preparation methods has been composed from 481 references, with a highlight of some promising methods fast developed during recent years and a somewhat brief introduction on most of the well-developed methods. All the samples were commonly referred to molecular composition, being extendable to particles including cells but not to organs, tissues and larger bodies. Some criteria to evaluate or validate a sample preparation method were proposed for reference. Strategy for integration of several methods to prepare complicated protein samples for proteomic studies was illustrated and discussed.

This investigation aimed at improving the performance of Taylor’s dispersion analysis for the fast and accurate measurement of diffusion coefficient of a minute solute in various solvents. The investigation was carried out on a capillary electrophoresis instrument by monitoring the UV absorption peak of a solute pulse and calculating the diffusion coefficient by peak efficiency. With L-phenylalanine as a main testing solute, some key factors were afterward disclosed including especially the capillary size, carrier flow velocity, injection volume and capillary conditioning. Peak tailing, large volume of sample injection and slow migration were found to underestimate the diffusion coefficient while very fast migration and high sample concentration caused overestimation. At a moderate flow velocity of 0.1–1 cm/s with a capillary of 72.44 μm I.D. ×60 cm (50 cm effective) maintained at 25°C, the diffusion coefficient of aqueous L-phenylalanine was determined, giving a value of 7.02×10−6 cm2/s with error <2% and relative standard deviation <0.2% (n=3). The method was shown to be applicable to the measurement of various samples such as aqueous phenylalanine, acetone, phenol, toluene and benzene, and nonaqueous benzene (in ethanol or 1-butanol).

A microwave-assisted method for rapid deposition of continuous gold films on glass substrates has been developed. Under microwave irradiation, gold nanoparticles in colloidal solutions were shown able to assemble on the naked substrates to form a gold monolayer within minutes. Images obtained by AFM revealed that the monolayer formed on the naked glass surface was much the same as that formed on the glass substrates pre-silanized with (3-aminopropyl)-trimethoxysilane. With this monolayer as seeds, further deposition of gold metal on the surface was thus possible and the thickness of the deposited gold was time-dependent as in the case of normal electroless plating. The sum time for preparing a 50-nm gold film on glass was about 15 minutes, much shorter than the existed electroless methods. Electrochemical experiments showed that the prepared gold films were continuous and can be used as stable electrodes able to sustain several hundreds of redox circulation. The quality of the films were also verified by surface plasmon resonance imaging (SPRI) studies and quite sharp pictures of protein dots were obtained, showing a smooth gold surface and proper film thickness were prepared.

A simple method is presented discriminating proteins at a gold surface by using an emerging technology, surface plasmon resonance (SPR) imaging. As a high throughput method, the protein array of bovine serum albumin (BSA), poly-l-lysine (PL), casein and lactate dehydrogenase (LDG) was fabricated and SPR imaging enables detection from different kinds of proteins immobilized on the sensor surface. These proteins can be discriminated directly by various reflected intensity or changing the incident angular position of light. Denaturation of these immobilized proteins on SPR sensor by interacting with denaturant 6 M GdnHCl solution was also performed and obvious changes in reflected intensity were occurred after denaturation. The observation of denaturation of these proteins further supported the fact that different proteins could be discriminated on protein array before denaturation. On the other hand, the procedure of denaturation provided useful information that any change of molecular structure with the progress of denaturation would result in change of SPR signal. Excellent reproducibility with a chip-to-chip for label-free discriminating various proteins was achieved.

In this article, the Poincare-Lighthill-Kuo (PLK) method is used to derive an analytical expression on the stability boundary and the ion trajectory. A multipole superposition model mainly including octopole component is adopted to represent the inhomogeneities of the field. In this method, both the motional displacement and secular frequency of ions have been expanded to asymptotic series by the scale of nonlinear term ε, which represents a weak octopole field. By solving the zero and first-order approximate equations, it is found that a frequency shift exists between the ideal and nonlinear conditions. The motional frequency of ions in nonlinear ion trap depends on not only Mathieu parameters, a and q, but also the percentage of the nonlinear field and the initial amplitude of ions. In the same trap, ions have the same mass-to-charge ratio (m/z) but they have different initial amplitudes or velocities. Consequently, they will be ejected at different time through after a mass-selective instability scan. The influences on the mass resolution in quadrupole ion trap, which is coupled with positive or negative octopole fields, have been discussed respectively.The shift of the stability boundary and frequency for nonlinear ion trap mass spectrometer has been investigated for improving the mass resolution.Download high-res image (144KB)Download full-size image

A one-step photochemical approach was established to quickly and specifically synthesize uniformly dispersed silver nanoparticles (AgNPs) on reduced graphene oxide (rGO) nanosheets. Silver–ammonia and graphene oxide (GO) were used as precursors to enhance the coordination-based adsorption of silver cations onto the negatively charged GO surface through ligation with ammonia, which could also continuously stabilize the nucleation and growth of AgNPs. The method allowed the easy control of the coverage percentage of AgNPs on rGO in a range from 7.2% to 81.6%. The prepared AgNPs-rGO composites were highly dispersible and stable in water in the absence of any stabilizing agent, and showed excellent catalytic properties in the reduction of 2-nitroaniline to 1,2-benzenediamine.