Ji

Gold Nanoparticle Assembly Microfluidic Reactor for Efficient On-line Proteolysis

A microchip reactor coated with a gold nanoparticle network entrapping trypsin was designed for the efficient on-line proteolysis of low level proteins and complex extracts originating from mouse macrophages. The nanostructured surface coating was assembled via a layer-by-layer electrostatic binding of poly(diallyldimethylammonium chloride) and gold nanoparticles. The assembly process was monitored by UV-visible spectroscopy, atomic force microscopy, and quartz crystal microbalance. The controlled adsorption of trypsin was theoretically studied on the basis of the Langmuir isotherm model, and the fitted Γmax and K values were estimated to be 1.2 × 10−7 mol/m2 and 4.1 × 105 m−1, respectively. An enzymatic kinetics assay confirmed that trypsin, which was entrapped in the biocompatible gold nanoparticle network with a high loading capacity, preserved its bioactivity. The maximum proteolytic rate of the adsorbed trypsin was 400 mm/(min·μg). Trace amounts of proteins down to femtomole per analysis were digested using the microchip reactor, and the resulting tryptic products were identified by MALDI-TOF MS/MS. The protein mixtures extracted from the mouse macrophages were efficiently identified by on-line digestion and LC-ESI-MS/MS analysis.

Enhanced Protein Digestion through the Confinement of Nanozeolite-Assembled Microchip Reactors

An on-chip microreactor was proposed toward the acceleration of protein digestion through the construction of a nanozeolite-assembled network. The nanozeolite microstructure was assembled using a layer-by-layer technique based on poly(diallyldimethylammonium chloride) and zeolite nanocrystals. The adsorption of trypsin in the nanozeolite network was theoretically studied based on the Langmuir adsorption isotherm model. It was found that the controlled trypsin-containing nanozeolite networks assembled within a microchannel could act as a stationary phase with a large surface-to-volume ratio for the highly efficient proteolysis of both proteins at low levels and with complex extracts. The maximum proteolytic rate of the adsorbed trypsin was measured to be 350 mM min-1 microg-1, much faster than that in solution. Moreover, due the large surface-to-volume ratio and biocompatible microenvironment provided by the nanozeolite-assembled films as well as the microfluidic confinement effect, the low-level proteins down to 16 fmol per analysis were confidently identified using the as-prepared microreactor within a very short residence time coupled to matrix-assisted laser desorption-time-of-flight mass spectrometry. The on-chip approach was further demonstrated in the identification of the complex extracts from mouse macrophages integrated with two-dimensional liquid chromatography-electrospray ionization-tandem mass spectrometry. This microchip reactor is promising for the development of a facile means for protein identification.

Proteolysis in microfluidic droplets: an approach to interface protein separation and peptide mass spectrometry.

A versatile microreactor protocol based on microfluidic droplets has been developed for on-line protein digestion. Proteins separated by liquid chromatography are fractionated in water-in-oil droplets and digested in sequence. The microfluidic reactor acts also as an electrospray ionization emitter for mass spectrometry analysis of the peptides produced in the individual droplets. Each droplet is an enzymatic micro-reaction unit with efficient proteolysis due to rapid mixing, enhanced mass transfer and automated handling. This droplet approach eliminates sample loss, cross-contamination, non-specific absorption and memory effect. A protein mixture was successfully identified using the droplet-based micro-reactor as interface between reverse phase liquid chromatography and mass spectrometry.

Multifunctional Paper Strip Based on Self-Assembled Interfacial Plasmonic Nanoparticle Arrays for Sensitive SERS Detection

A smart and multifunctional paper-based SERS sensing card is generated through patterning self-assembled interfacial arrays of gold nanoparticles (AuNPs) on the tip of an arrow-shaped paper strip. It is found that the closely packed monolayer of AuNPs is evenly distributed on the paper surface, resulting in a multitude of SERS hot spots over the detection zone. The paper card, with its inherent ability to separate and preconcentrate analytes by the capillary force and polarity difference between sample components, was exploited successfully as an integrated platform, allowing for sub-attomolar (50 × 10(-18) M) detection from microliter-volume (10 μL) samples. Furthermore, the simple preparation (lithography-free process), fast detection (<5 min), and low cost (<3 cents) demonstrate that the paper card is a practical and portable sensing interface for wide application in environmental and food analysis.

A three-dimensional silver nanoparticles decorated plasmonic paper strip for SERS detection of low-abundance molecules.

The fabrication of SERS substrates, which can offer the advantages of strong Raman signal enhancement with good reproducibility and low cost, is still a challenge for practical applications. In this work, a simple three-dimensional (3D) paper-based SERS substrate, which contains plasmonic silver-nanoparticles (AgNPs), has been developed by the silver mirror reaction. This paper strip was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), etc. Pretreatment of the paper as well as the reaction time, temperature, and reagent concentrations for the silver mirror reaction were varied for further studies. With the optimized experimental parameters, the AgNPs synthesized and distributed in-situ on the paper strip could give more favorable SERS performance. The limit of detection (LOD) as low as 10(-11)M for Rhodamine 6G (R6G) and 10(-9)M for p-aminothiophenol (p-ATP) plus wide linear range for the log-log plot of Raman intensity versus analyte concentration were achieved. The detection of R6G in rain water was also carried out successfully. The merits of this protocol include low cost, easy operation, high sensitivity and acceptable stability, which make it ideal for the detection of environmental samples in trace amounts.

Interfacial Self-Assembled Functional Nanoparticle Array: A Facile Surface-Enhanced Raman Scattering Sensor for Specific Detection of Trace Analytes

Surface-enhanced Raman scattering (SERS) has proven to be promising for the detection of trace analytes; however, the precise nanofabrication of a specific and sensitive plasmonic SERS-active substrate is still a major challenge that limits the scope of its applications. In this work, gold nanoparticles are self-assembled into densely packed two-dimensional arrays at a liquid/liquid interface between dimethyl carbonate and water in the absence of template controller molecules. Both the simulation and experiment results show that the particles within these film-like arrays exhibit strong electromagnetic coupling and enable large amplification of Raman signals. In order to realize the level of sensing specificity, the surface chemistry of gold nanoparticles (Au NPs) is rationally tailored by incorporating an appropriate chemical moiety that specifically captures molecules of interest. The ease of fabrication and good uniformity make this platform ideal for in situ SERS sensing of trace targets in complex samples.

High-Resolution and Universal Visualization of Latent Fingerprints Based on Aptamer-Functionalized Core-Shell Nanoparticles with Embedded SERS Reporters.

Although fingerprints have been widely used in forensic investigations, low resolution and poor universality are still the main obstacles for the development of fingerprint visualization. In this paper, a facile and universal imaging protocol for latent fingerprints (LFPs) was developed by combining sandwiched SERS probes with the highly sensitive and selective recognition of aptamers. The embedded SERS probes (Au/pNTP/SiO2) successfully avoid the environment interference, ascertaining the stability and reproducibility of Raman signals, and simultaneously improve the efficiency of the fingerprint identification. This approach is operationally simple without complicated pre- or post-treatments. Moreover, the fingerprint images display the high resolution in which third-level details can be clearly identified. This is a general approach and can be used to detect various types of fingerprints, including sebaceous, eccrine, fresh LFPs, and aged LFPs on different substrates (such as smooth, scratching, semiporous, and porous surfaces).

Quantitative label-free and real-time surface-enhanced Raman scattering monitoring of reaction kinetics using self-assembled bifunctional nanoparticle arrays.

Although surface-enhanced Raman scattering (SERS) has proven to be an effective tool for label-free monitoring of catalytic reactions, quantitative characterization of reaction kinetics via this technique remains challenging owing to the difficulty in integrating catalytic and plasmonic activities into a single platform. In this work, we report on an easy access to highly sensitive plasmonic nanoarrays for direct and label-free monitoring of a gold-catalyzed reaction by SERS. The hierarchically structured three-dimensional assemblies, which consist of small gold catalyst nanoparticles distributed on a self-assembled monolayer of larger gold nanoparticles, were formed through a simple and rapid stepwise interfacial self-assembling process (fabrication time <10 min). The well-defined interparticle distances (<1 nm) lead to efficient plasmonic coupling and ensure both catalytic and SERS-active sites exposed to the environment. Such a versatile bifunctional platform thus allows quantitative determination of the rate constant and activation energy of the catalytic reaction with SERS.

Simultaneous Online Enrichment and Identification of Trace Species Based on Microfluidic Droplets

A facile online enrichment protocol has been proposed based on microfluidic droplets acting as an interface between a liquid chromatography separation system and detection systems of ESI-MS/MS and laser-induced fluorescence. Low-abundance species were successfully concentrated and analyzed in this system via droplet shrinkage. The proposed platform significantly increased the enrichment efficiency and detection sensitivity with reduced sample handling steps, short analysis time, and no cross-contamination. The presented system is universal, shows no discrimination, and is easily coupled with other separation and detection approaches.

Ambient ionization based on mesoporous graphene coated paper for therapeutic drug monitoring

Paper spray (PS), as a new ambient ionization method, has been applied for direct qualitative and quantitative analysis. The high sensitivity and minimum internal energy (low spray voltage) with optimized paper spray conditions is a significant request for real application in POCT. In this study, a simple and efficient ambient ionization method is developed by spraying from a mesoporous graphene foams (MGFs)-modified paper surface. The good electrical conductivity of MGFs results in obvious spray voltage decrease. Meanwhile, the MGFs-paper substrate has a well improvement in separation and elution efficiency ascribing to ultrahigh specific surface area and π-π electrostatic stacking property of graphene. In combination a commercial triple quadrupole mass spectrometer, the paper spray is successfully used for analysis of amphetamine in saliva. The linear dynamic ranges expand 10 fold in comparison with unmodified chromatography papers and the low limit of quantitation (LOQ) is as low as 1 pg/mL. A small sample volume (0.5 μL) could be analyzed immediately after spotting, without any pretreatment. The performance of this method was demonstrated for application in fast point-of-care mass spectrometry.