Jiangjiang Liu

Development, characterization, and application of paper spray ionization.

Paper spray is developed as a direct sampling ionization method for mass spectrometric analysis of complex mixtures. Ions of analyte are generated by applying a high voltage to a paper triangle wetted with a small volume (<10 microL) of solution. Samples can be preloaded onto the paper, added with the wetting solution, or transferred from surfaces using the paper as a wipe. It is demonstrated that paper spray is applicable to the analysis of a wide variety of compounds, including small organic compounds, peptides, and proteins. Procedures are developed for analysis of dried biofluid spots and applied to therapeutic drug monitoring with whole blood samples and to illicit drug detection in raw urine samples. Limits of detection of 50 ng/mL (or 20 pg absolute) are achieved for atenolol in bovine blood. The combination of sample collection from surfaces and paper spray ionization also enables fast chemical screening at high sensitivity, for example 100 pg of heroin distributed on a surface and agrochemicals on fruit peels are detectable. Online derivatization with a preloaded reagent is demonstrated for analysis of cholesterol in human serum. The combination of paper spray with miniature mass spectrometers offers a powerful impetus to wide application of mass spectrometry in nonlaboratory environments.

Leaf Spray: Direct Chemical Analysis of Plant Material and Living Plants by Mass Spectrometry

The chemical constituents of intact plant material, including living plants, are examined by a simple spray method that provides real-time information on sugars, amino acids, fatty acids, lipids, and alkaloids. The experiment is applicable to various plant parts and is demonstrated for a wide variety of species. An electrical potential is applied to the plant and its natural sap, or an applied solvent generates an electrospray that carries endogenous chemicals into an adjacent benchtop or miniature mass spectrometer. The sharp tip needed to create a high electric field can be either natural (e.g., bean sprout) or a small nick can be cut in a leaf, fruit, bark, etc. Stress-induced changes in glucosinolates can be followed on the minute time scale in several plants, including potted vegetables. Differences in spatial distributions and the possibility of studying plant metabolism are demonstrated.

Quantitative paper spray mass spectrometry analysis of drugs of abuse

An ambient method for rapid monitoring and quantitation of drugs of abuse in dried blood spots was developed using paper spray tandem mass spectrometry (PS-MS).

Biological Tissue Diagnostics Using Needle Biopsy and Spray Ionization Mass Spectrometry

Needle biopsy is a routine medical procedure for examining tissue or biofluids for the presence of disease using standard methods of pathology. In this work, spray ionization directly from tissue in the biopsy needle is shown to provide highly specific molecular information through mass spectrometry analysis. The data are available within a minute after the tissue biopsy, a time scale that allows immediate medical decisions to be made. This method has been performed for tissues in a variety of organs including brain, liver, kidney, adrenal gland, stomach, and spinal cord. Amino acids, hormones, fatty acids, anesthetics, and phospholipids are detected from the tissues and identified using exact mass measurement and tandem mass spectrometry. Lipid profiles are rich in information and, as in imaging MS methods, they have the potential to serve to distinguish diseased from healthy tissue. Needle biopsies allow a crude form of depth profiling that is demonstrated with the analysis of tissue samples taken by a needle inserted into a porcine kidney at various depths.

Analysis of Biological Samples Using Paper Spray Mass Spectrometry: An Investigation of Impacts by the Substrates, Solvents and Elution Methods

Paper spray has been developed as a fast sampling ionization method for direct analysis of raw biological and chemical samples using mass spectrometry (MS). Quantitation of therapeutic drugs in blood samples at high accuracy has also been achieved using paper spray MS without traditional sample preparation or chromatographic separation. The paper spray ionization is a process integrated with a fast extraction of the analyte from the raw sample by a solvent, the transport of the extracted analytes on the paper, and a spray ionization at the tip of the paper substrate with a high voltage applied. In this study, the influence on the analytical performance by the solvent–substrate systems and the selection of the elution methods was investigated. The protein hemoglobin could be observed from fresh blood samples on silanized paper or from dried blood spots on silica-coated paper. The on-paper separation of the chemicals during the paper spray was characterized through the analysis of a mixture of the methyl violet 2B and methylene blue. The mode of applying the spray solvent was found to have a significant impact on the separation. The results in this study led to a better understanding of the analyte elution, on-paper separation, as well as the ionization processes of the paper spray. This study also helps in establishing a guideline for optimizing the analytical performance of paper spray for direct analysis of target analytes using mass spectrometry.

Fabrication of microwell arrays based on two-dimensional ordered polystyrene microspheres for high-throughput single-cell analysis.

This paper describes a method of fabricating rounded bottom microwell arrays (MA) in poly(dimethylsiloxane) (PDMS) by molding a monolayer of ordered polystyrene (PS) microspheres. PS microspheres were self-assembled on a glass slide and partially melted mainly from the bottom at 240 °C to increase adhesive force with the substrate. The partially melted PS arrays were used as master to generate MA. Microwell sizes are tunable in the 10-20 μm range with rounded bottoms; such a 3D structure is not readily obtainable through conventional soft lithography. Both adherent and nonadherent cell types can be retained in the microwells with high efficiency. As a demonstration of the advantage of real-time cell screening with this MA, single cell enzyme kinetic analysis was also carried out on trapped single cells. The PDMS MA may find applications in high-throughput drug screening, guided formation of cell clusters, and multicellular communication.

Direct mass spectrometry analysis of biofluid samples using slug-flow microextraction nano-electrospray ionization.

Direct mass spectrometry (MS) analysis of biofluids with simple procedures represents a key step in the translation of MS techniques to clinical and point-of-care applications. The current study reports the development of a single-step method using slug-flow microextraction and nano-electrospray ionization for MS analysis of organic compounds in blood and urine. High sensitivity and quantitation precision have been achieved in the analysis of therapeutic and illicit drugs in 5 μL samples. Real-time chemical derivatization has been incorporated for analyzing anabolic steroids. The monitoring of enzymatic functions has also been demonstrated with cholinesterase in wet blood. The reported study encourages the future development of disposable cartridges, which function with simple operation to replace the traditional complex laboratory procedures for MS analysis of biological samples.

Enabling quantitative analysis in ambient ionization mass spectrometry: internal standard coated capillary samplers.

We describe a sampling method using glass capillaries for quantitative analysis of trace analytes in small volumes of complex mixtures (~1 μL) using ambient ionization mass spectrometry. The internal surface of a sampling glass capillary was coated with internal standard then used to draw liquid sample and so transfer both the analyte and internal standard in a single fixed volume onto a substrate for analysis. The internal standard was automatically mixed into the sample during this process and the volumes of the internal standard solution and sample are both fixed by the capillary volume. Precision in quantitation is insensitive to variations in length of the capillary, making the preparation of the sampling capillary simple and providing a robust sampling protocol. Significant improvements in quantitation accuracy were obtained for analysis of 1 μL samples using various ambient ionization methods.

A microfluidic approach for anticancer drug analysis based on hydrogel encapsulated tumor cells

A novel method based on fluorescence detection of hydrogel encapsulated cells in microchannels was developed for anticancer drug analysis. In this work, human hepatoma HepG2 cells and human lung epithelial A549 cells were simultaneously immobilized inside two different shapes of three-dimensional hydrogel microstructures using photolithography approach on a same array. Microarrays of living cells offer the potential for parallel detection of many cells and thereby enable high-throughput assays. Using a photolithographic setup, we investigated the prepolymer composition and crosslinking parameters that influenced cell viability inside photocrosslinked hydrogels. The viability of cells encapsulated inside hydrogel microstructures was higher than 90% under optimized photocrosslinking conditions. The cells were further cultured under stable conditions and remained viable for at least three days that were able to carry out cell-based assays. Furthermore, we studied the variation of two intracellular redox parameters (glutathione and reactive oxygen species) in anticancer drug-induced apoptosis in HepG2 and A549 cells. Two anticancer drugs exhibited distinct effects on the levels of intracellular glutathione and reactive oxygen species, indicating the selectivity of these drugs on the disturbance of redox balance within cells. The established platform provides a convenient and fast method for monitoring the effect of anticancer drugs on tumor cells, which is very useful for fundamental biomedical research.

A simple microfluidic chlorine gas sensor based on gas–liquid chemiluminescence of luminol-chlorine system

In this work, a microfluidic chlorine gas sensor based on gas-liquid interface absorption and chemiluminescence detection was described. The liquid chemiluminescence reagent-alkaline luminol solution can be stably sandwiched between two convex halves of a microchannel by surface tension. When chlorine gas was introduced into the micro device, it was dissolved into the interfacial luminol solution and transferred to ClO(-), and simultaneously luminol was excited and chemiluminescence emitted. The emitted chemiluminescence light was perpendicularly detected by a photomultiplier tube on a certain detection region. The remarkable advantage of the detection system is that both adsorption and detection were carried out at the gas-liquid interface, which avoids the appearance of bubbles. The whole analytical cycle including filling CL reagent, sample injection, CL detection and emptying the device was as short as 30 s. The linear concentration range of chlorine gas detection with direct introduction of sample method is from 0.5 to 478 ppm. The detection limit of this method is 0.2 ppm for standard chlorine gas and the relative standard deviation of five determinations of 3.19 ppm spiked chlorine sample was 5.2%.