Browsing by Author "Chen, Yu-Chie"

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A compact 3D-printed interface for coupling open digital microchips with Venturi easy ambient sonic-spray ionization mass spectrometry
(2015-01-01)
Hu, Jie-Bi
;
Chen, Ting-Ru
;
Chang, Chia-Hsien
;
Cheng, Ji-Yen
;
Chen, Yu-Chie
Digital microfluidics (DMF) based on the electrowetting-on-dielectric phenomenon is a convenient way of handling microlitre-volume aliquots of solutions prior to analysis. Although it was shown to be compatible with on-line mass spectrometric detection, due to numerous technical obstacles, the implementation of DMF in conjunction with MS is still beyond the reach of many analytical laboratories. Here we present a facile method for coupling open DMF microchips to mass spectrometers using Venturi easy ambient sonic-spray ionization operated at atmospheric pressure. The proposed interface comprises a 3D-printed body that can easily be "clipped" at the inlet of a standard mass spectrometer. The accessory features all the necessary connections for an open-architecture DMF microchip with T-shaped electrode arrangement, thermostatting of the microchip, purification of air (to prevent accidental contamination of the microchip), a Venturi pump, and two microfluidic pumps to facilitate transfer of samples and reagents onto the microchip. The system also incorporates a touch-screen panel and remote control for user-friendly operation. It is based on the use of popular open-source electronic modules, and can readily be assembled at low expense.
A hybrid nanoparticle matrix for mass spectrometry
(2013)
Li, Po-Han
;
Huang, Shin-Yi
;
Chen, Yu-Chie
;
Urban, Pawel L.
;
應用化學系
We demonstrate hybrid inorganic-organic nanoparticles -based on silicon dioxide and 9-aminoacridine- which can enhance mass spectrometric analysis and imaging in the negative-ion mode. The nanoparticles bind to the surface of cells while still in the liquid phase, which is followed by a controlled release of the organic matrix molecules triggered by alkaline ammonia vapours delivered to the specimen in a closed chamber. First, the method was optimized and tested using standard compounds as analytes. Second, the spatial resolution was verified using a natural fibre (diameter similar to 20 mu m). Third, the method was used in the imaging of molecules present in the outer layer of large algal cells (Closterium acerosum). An important advantage of this method is that nanoparticles loaded with organic matrix can be applied to the biological cells as aqueous suspensions; hence, the release and spreading of metabolites can be limited during sample preparation for MALDI-MS. In addition, since this method does not involve spraying, exposure of experimenters to toxic aerosols is decreased.
A label-free sensing method for phosphopeptides using two-layer gold nanoparticle-based localized surface plasma resonance spectroscopy
(2011-01-01)
Chen, Jen-Yi
;
Chen, Yu-Chie
;
應用化學系
;
Department of Applied Chemistry
In this study, a new type of localized surface plasmon resonance (LSPR) sensing substrate for phosphopeptides was explored. It has been known that LSPR response for target species is larger in the near-infrared region (NIR) than in the visible region of the electromagnetic spectrum. Several types of noble metal nanoparticles (NPs) with NIR absorption capacities have been previously demonstrated as effective LSPR-sensing nanoprobes. Herein, we demonstrate a straightforward approach with improved sensitivity by simply using layer-by-layer (LBL) spherical Au NPs self-assembled on glass slides as the LSPR-sensing substrates that are responsive in the NIR region of the electromagnetic spectrum. The modified glass slide acquired an LSPR absorption band in the NIR, which resulted from the dipole-dipole interactions between Au NPs. To enable the chip to sense phosphopeptides, the surface of the glass chip was spin-coated with thin titania film (TiO(2)-Glass@Au NPs). Absorption spectrophotometry was employed as a detection tool. Tryptic digest of alpha-casein was used as a model sample. The feasibility of using the new LSPR approach for detecting a potential risk factor leading to cancers (i.e., phosphorylated fibrinopeptide A) directly from human serum samples was demonstrated. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was used to confirm the results.
A two-matrix system for MALDI MS analysis of serine phosphorylated peptides concentrated by Fe3O4/Al2O3 magnetic nanoparticles
(2008-04-01)
Chen, Cheng-Tai
;
Chen, Yu-Chie
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Acceleration of microwave-assisted enzymatic digestion reactions by magnetite beads
(2007-03-15)
Chen, Wei-Yu
;
Chen, Yu-Chie
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
In this study, we demonstrated that microwave-assisted enzymatic digestion could be greatly accelerated by multifunctional magnetite beads. The acceleration of microwave-assisted enzymatic digestion by the presence of the magnetite beads was attributable to several features of the beads. Their capacity to absorb microwave radiation leads to rapid heating of the beads. Furthermore, their negatively charged functionalities cause adsorption of proteins with opposite charges onto their surfaces by electrostatic interactions, leading to a concentration on the surfaces of the beads of proteins present in trace amounts in the solution. The adsorbed proteins are denatured and hence rendered vulnerable to enzymatic digestion and are digested on the beads. For microwave heating, 30 s was sufficient for carrying out the tryptic digestion of cytochrome c, in the presence of magnetite beads, while 1 min was adequate for tryptic digestion of myoglobin. The digestion products were characterized by MALDI-MS. This rapid enzymatic digestion allowed the entire time for identification of proteins to be greatly reduced. Furthermore, specific proteins present in trace quantities were enriched from the sample on the magnetite beads and could be rapidly isolated from the sample by employing an external magnetic field. These multiple roles of magnetite beads, as the absorber for microwave irradiation, the concentrating probe, and the agent for unfolding proteins, contributed to their capability of accelerating microwave-assisted enzymatic digestion. We also demonstrated that trypsin immobilized magnetite beads were suitable for use in microwave-assisted enzymatic digestion.
Affinity capture of uropathogenic Escherichia coli using pigeon ovalbumin-bound Fe(3)O(4)@Al(2)O(3) magnetic nanoparticles
(2008-07-15)
Liu, Jr-Chi
;
Tsai, Pei-Jane
;
Lee, Yuan C.
;
Chen, Yu-Chie
;
應用化學系
Escherichia coli and Staphylococcus saprophyticus are the most common causes of urinary tract infections, with 80% of these infections caused by uropathogenic E. coli. Because the P fimbriae of E. coli have specificity toward Gal(alpha 1-4)Gal beta units, pigeon ovalbumin (POA), whose structure contains terminal Gal(alpha 1-4)Gal beta moieties, was used as a probe for interaction with P fimbriated E. coli. The functional affinity probes for these bacteria by immobilizing POA-a phosphoprotein-onto the surface of magnetic iron oxide nanoparticles (NPs) coated with alumina (Fe(3)O(4)@Al(2)O(3)), using the phosphate units of POA as linking groups for the formation of phosphate-alumina complexes. The immobilization process occurred within 30 s when performing the reaction under microwave heating. The magnetic POA-Fe(3)O(4)@Al(2)O(3) NPs generated using this facile approach exhibited specificity toward P fimbriated E. coli. The bacteria targeted by the affinity probes were characterized by matrix-assisted laser desorption/ionization mass spectrometry. The detection limit toward uropathogenic bacteria when using this approach was similar to 9.60 x 10(4) cfu/mL (0.5 mL).
Affinity capture of uropathogenic Escherichia coli using pigeon ovalbumin-bound Fe3O4@Al2O3 magnetic nanoparticles
(2008-07-15)
Liu, Jr-Chi
;
Tsai, Pei-Jane
;
Lee, Yuan C.
;
Chen, Yu-Chie
;
應用化學系
Escherichia coli and Staphylococcus saprophyticus are the most common causes of urinary tract infections, with 80% of these infections caused by uropathogenic E. coli. Because the P fimbriae of E. coli have specificity toward Gal(alpha 1-4)Gal beta units, pigeon ovalbumin (POA), whose structure contains terminal Gal(alpha 1-4)Gal beta moieties, was used as a probe for interaction with P fimbriated E. coli. The functional affinity probes for these bacteria by immobilizing POA-a phosphoprotein-onto the surface of magnetic iron oxide nanoparticles (NPs) coated with alumina (Fe3O4@Al2O3), using the phosphate units of POA as linking groups for the formation of phosphate-alumina complexes. The immobilization process occurred within 30 s when performing the reaction under microwave heating. The magnetic POA-Fe3O4@Al2O3 NPs generated using this facile approach exhibited specificity toward P fimbriated E. coli. The bacteria targeted by the affinity probes were characterized by matrix-assisted laser desorption/ionization mass spectrometry. The detection limit toward uropathogenic bacteria when using this approach was similar to 9.60 x 10(4) cfu/mL (0.5 mL).
Affinity capture using peptide-functionalized magnetic nanoparticles to target Staphylococcus aureus
(2016)
Kuo, Fang-Yin
;
Lin, Wei-Lien
;
Chen, Yu-Chie
;
應用化學系
;
應用化學系分子科學碩博班
Staphylococcus aureus, a commonly found pathogen, can cause food poisoning and infections. Thus, it is necessary to develop analytical methods for the rapid screening of S. aureus in suspicious samples. Magnetic nanoparticles (MNPs) are widely used as affinity probes to selectively enrich target species from complex samples because of their high specific surface area and magnetic properties. The MNP surface should be functionalized to have the capability to target specific species. We herein propose a straightforward method to functionalize aluminum oxide-coated iron oxide (Fe3O4@Al2O3) MNPs with the peptide HHHHHHDEEGLFVD (D). The peptide D was comprised of three domains: polyhistidine (H-6) used as the linker, DEE added as the spacer, and GLFVD used for targeting S. aureus. D was immobilized on the surface of Fe3O4@Al2O3 MNPs through H-6-Al chelation. Our results showed that the D-functionalized Fe3O4@Al2O3 MNPs (D-Fe3O4 MNPs) possess the capability to target S. aureus. The selective trapping experiments were conducted under microwave-heating for only 60 s, and sufficient bacterial cells were trapped by the MNPs to be identified by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). We demonstrated that the D-Fe3O4@Al2O3 MNPs combined with MALDI-MS can be used to rapidly characterize trace amounts of S. aureus in complex juice and egg samples.
Affinity-based mass spectrometry using magnetic iron oxide particles as the matrix and concentrating probes for SALDI MS analysis of peptides and proteins
(2006-10-01)
Chen, Wei-Yu
;
Chen, Yu-Chie
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Silane-immobilized magnetic iron oxide particles were used as the assisting material in surface-assisted laser desorption/ionization (SALDI) mass spectrometric analysis. This approach can be used to analyze small proteins and peptides. The upper detectable mass range is approximately 16 kDa. The detection limit for peptides is about 20 fmol. Silanized iron oxide particles with negatively charged functionalities can also be used as the affinity probes to selectively trap oppositely charged species from sample solutions by adjusting the pH of the solution. A tryptic digest product of cytochrome C at a concentration as low as 10 nM can be enriched by the particles and directly analyzed by iron oxide SALDI MS without the need for elution steps. Affinity-based mass spectrometry using the bifunctional silanized magnetic iron oxide particles as the SALDI matrix and concentrating probe is demonstrated in this study.
Analysis of volatile compounds by open-air ionization mass spectrometry
(2017-05-08)
Meher, Anil Kumar
;
Chen, Yu-Chie
;
應用化學系
;
Department of Applied Chemistry
This study demonstrates a simple method for rapid and in situ identification of volatile and endogenous compounds in culinary spice samples through mass spectrometry (MS). This method only requires a holder for solid spice sample (2-3 mm) that is placed close to a mass spectrometer inlet, which is applied with a high voltage. Volatile species responsible for the aroma of the spice samples can be readily detected by the mass spectrometer. Sample pretreatment is not required prior to MS analysis, and no solvent was used during MS analysis. The high voltage applied to the inlet of the mass spectrometer induces the ionization of volatile compounds released from the solid spice samples. Furthermore, moisture in the air also contributes to the ionization of volatile compounds. Dried spices including cinnamon and cloves are used as the model sample to demonstrate this straightforward MS analysis, which can be completed within few seconds. Furthermore, we also demonstrate the suitability of the current method for rapid screening of cinnamon quality through detection of the presence of a hepatotoxic agent, i.e. coumarin. (C) 2017 Elsevier B.V. All rights reserved.
Antibacterial gold nanoparticle-based photothermal killing of vancomycin-resistant bacteria
(2018-06-01)
Wang, Sin-Ge
;
Chen, Yen-Chun
;
Chen, Yu-Chie
;
應用化學系
;
Department of Applied Chemistry
Aim: The extensive use of vancomycin has given rise to vancomycin-resistant bacterial strains, such as vancomycin-resistant Enterococci (VRE). We aim to explore potent medical treatments that can inhibit the growth of VRE. Materials & methods: Vancomycin-immobilized gold nanoparticles (Au@Van NPs) with polygonal shapes from one-pot reactions were generated within approximately 7 min. Results & discussion: The as-prepared Au NPs exhibit not only antibacterial capability but also photothermal competence. The temperature of the sample solution containing the as-prepared Au@Van NPs can be raised by approximately 15 degrees C under irradiation by a near-infrared laser (lambda = 808 nm) within 5 min. Conclusion: The required amount of vancomycin on the as-prepared Au@Van NPs combined with near-infrared irradiation for inhibiting VRE is approximately 16-fold lower than that of free-form vancomycin.
Automated system for extraction and instantaneous analysis of millimeter-sized samples
(2014)
Hu, Jie-Bi
;
Chen, Ssu-Ying
;
Wu, June-Tai
;
Chen, Yu-Chie
;
Urban, Pawel L.
Adequate sample treatment is critical when employing mass spectrometry (MS) in the analyses of complex biological matrices. Despite various improvements, it is generally difficult to automate the process of preparing solid biological samples for MS analysis. Here we demonstrate a facile approach for automation of the whole analysis (from an untreated sample to the final result). The proposed platform enables disruption and extraction of relatively small samples (individual fruit flies, fragments of tea leaves, powdered drug sampled with a cotton bud), and almost simultaneous analysis of the obtained extract within less than 10 min, and with very little intervention of the analyst. The operation is straightforward: once a sample is placed in the sample chamber, the analyst only needs to press a button on the touch screen of the user interface. The programmed open-source electronic device triggers addition of a small amount of solvent, and subsequent mechanical disruption/extraction of the specimen under controlled conditions (thermostated chamber). A small volume of the extract is directed to the ion source of the mass spectrometer incorporating a Venturi pump. During the operation of the instrument, fluorescence intensities (excitation wavelength windows: 320-380 and 460-500 nm) as well as MS extracted ion currents are recorded simultaneously. In the case of fruit fly samples, similar to 70 signals were recorded in both modes while the analysis of green tea leaves yielded similar to 30 signals. The resulting data reveal time-resolved extraction profiles characterizing every sample.
Automatic Sampling and Analysis of Organics and Biomolecules by Capillary Action-Supported Contactless Atmospheric Pressure Ionization Mass Spectrometry
(2013-06-06)
Hsieh, Cheng-Huan
;
Meher, Anil Kumar
;
Chen, Yu-Chie
;
應用化學系
;
Department of Applied Chemistry
Contactless atmospheric pressure ionization (C-API) method has been recently developed for mass spectrometric analysis. A tapered capillary is used as both the sampling tube and spray emitter in C-API. No electric contact is required on the capillary tip during C-API mass spectrometric analysis. The simple design of the ionization method enables the automation of the C-API sampling system. In this study, we propose an automatic C-API sampling system consisting of a capillary (similar to 1 cm), an aluminium sample holder, and a movable XY stage for the mass spectrometric analysis of organics and biomolecules. The aluminium sample holder is controlled by the movable XY stage. The outlet of the C-API capillary is placed in front of the orifice of a mass spectrometer, whereas the sample well on the sample holder is moved underneath the capillary inlet. The sample droplet on the well can be readily infused into the C-API capillary through capillary action. When the sample solution reaches the capillary outlet, the sample spray is readily formed in the proximity of the mass spectrometer applied with a high electric field. The gas phase ions generated from the spray can be readily monitored by the mass spectrometer. We demonstrate that six samples can be analyzed in sequence within 3.5 min using this automatic C-API MS setup. Furthermore, the well containing the rinsing solvent is alternately arranged between the sample wells. Therefore, the C-API capillary could be readily flushed between runs. No carryover problems are observed during the analyses. The sample volume required for the C-API MS analysis is minimal, with less than 1 nL of the sample solution being sufficient for analysis. The feasibility of using this setup for quantitative analysis is also demonstrated.
Bright carbon dots as fluorescence sensing agents for bacteria and curcumin
(2017-09-01)
Baig, Mirza Muhammad Fahad
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Chen, Yu-Chie
;
應用化學系
;
Department of Applied Chemistry
Carbon dots (C-dots) are fluorescent nanomaterials that possess good photostability and low toxicity. They have been used as sensing probes and bioimaging agents for a variety of biological species. Numerous methods are available to generate C-dots. Nevertheless, simple and straightforward synthesis methods must be explored for the synthesis of C-dots from inexpensive, natural sources. In this study, we developed a simple method to generate C-dots from inexpensive chicken egg whites through a one-step heating reaction. The size of the generated C-dots was 3.3 +/- 0.4 nm, and the quantum yield of the C-dots was as high as similar to 43%. The as-prepared C-dots can be used as multicolor labeling agents for bacteria such as Staphylococcus aureus and Escherichia coli. Furthermore, the generated C-dots can be used as Forster resonance energy transfer sensing probes for curcumin, which is an active ingredient of turmeric and medicinal pigment. The feasibility of using the C-dots as selective sensing probes to determine the amount of curcumin from complex turmeric powder and condensed turmeric tablets is also demonstrated. (C) 2017 Elsevier Inc. All rights reserved.
Capillary Action-Supported Contact less Atmospheric Pressure Ionization for the Combined Sampling and Mass Spectrometric Analysis of Biomolecules
(2011-04-15)
Hsieh, Cheng-Huan
;
Chang, Chia-Hsien
;
Urban, Pawel L.
;
Chen, Yu-Chie
;
應用化學系
It is proposed that a short tapered capillary can be utilized as a nanoliter-volume sampling tool and sample emitter for generation of gas-phase ions in front of the mass spectrometer, without the need for using an additional electric power supply, a gas supply, or a syringe pump. A wide range of molecules can be analyzed in pure solutions and complex matrixes (cell extract, urine, and plant tissue) with no or minimum sample preparation. Singly and multiply charged ions can be detected in either positive or negative-ion mode. Because of the nanoliter-volume sampling and low spectral background, the mass detection limit for bradykinin is in the low attomole range. Other advantages include simplicity, disposability, and low cost. The putative mechanism of the ion formation in this capillary-action supported contactless spray emitter is discussed.
Capillary hydrodynamic chromatography reveals temporal profiles of cell aggregates
(2016-03-03)
Tang, Ya-Ru
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Huang, Hsin-Yi
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Hu, Jie-Bi
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Rattinam, Rajesh
;
Li, Chun-Hsien
Microbial cells are known to form aggregates. Such aggregates can be found in various matrices; for example, functional drinks. Capillary hydrodynamic chromatography (HDC) enables separation of particles by size using nanoliter-scale volumes of samples. Here we propose an approach based on HDC for characterisation of real samples containing aggregated and non-aggregated bacterial and fungal cells. Separation of cells and cell aggregates in HDC arises from the parabolic flow profile under laminar flow conditions. In the presented protocol, hydrodynamic separation is coupled with different on-line and offline detectors (light absorption/scattering and microscopy). The method has successfully been applied in the monitoring of dynamic changes in the microbiome of probiotic drinks. Chromatographic profiles of yogurt and kefir samples obtained at different times during fermentation are in a good agreement with microscopic images. Moreover, thanks to the implementation of an area imaging detector, capillary HDC could be multiplexed and used to profile spatial gradients in cell suspensions, which arise in the course of sedimentation of cells and cell aggregates. This result shows compatibility of sedimentation analysis and capillary HDC. We believe that the approach may find applications in the profiling of functional foods and other matrices containing aggregated bioparticles. (C) 2016 Elsevier B.V. All rights reserved.
Carbon fiber ionization mass spectrometry coupled with solid phase microextraction for analysis of Benzo[a]pyrene
(2019-02-21)
Wu, Min-Li
;
Chen, Te-Yu
;
Chen, Wen-Jie
;
Baig, Mirza Muhammad Fahad
;
Wu, Yi-Cheng
Solid phase micro-extraction (SPME) is an effective technique that can be used to selectively enrich trace analytes of interest from complex samples. Owing to its high sensitivity and high selectivity, mass spectrometry (MS) has been widely used as the detection tool to confirm the analytes enriched on SPME fibers. Generally, thermal desorption or solvent desorption is used to desorb analytes from SPME fibers for MS analysis. A straightforward ionization method called carbon fiber ionization (CFI), which uses a single carbon fiber (diameter: similar to 10 mu m) as ionization emitter in MS, has been demonstrated lately. Analytes adsorbed on the carbon fiber, which is placed close (similar to 5 mm) to the inlet of a mass spectrometer, can be readily ionized through corona discharge and detected by the mass spectrometer. One unique feature regarding this approach over other existing ambient ionization methods is that no additional electric contact is applied directly on the carbon fiber. Nevertheless, on the basis of the electric field provided by the mass spectrometer, corona discharge can readily occur for ionizing analytes on the carbon fiber. Carbon fiber has high affinity toward polycyclic aromatic hydrocarbons due to its graphite-like surface structure. We herein explore a hyphenated-technique by combining carbon-fiber based SPME with CFI-MS for extraction of benzo[a]pyrene (BaP), a carcinogen, from aqueous samples. After BaP are adsorbed on a carbon fiber through SPME, the SPME carbon fiber can be readily placed in front of the mass spectrometer for MS analysis. The ions at m/z 252 derived from BaP adsorbed on the carbon fiber can be immediately acquired by the mass spectrometer without the requirement of applying heating or solvent. The limit of detection of BaP using the developed method was as low as similar to 60 pM. It is also feasible to detect BaP from complex serum sample. The feasibility of using the approach for quantitative analysis of BaP was also demonstrated. The linear dynamic range toward BaP was 0.2-5 nM. The extraction efficiency using this approach for aqueous samples was similar to 91%. (C) 2018 Elsevier B.V. All rights reserved.
Carbon Fiber Ionization Mass Spectrometry for the Analysis of Analytes in Vapor, Liquid, and Solid Phases
(2017-12-19)
Wu, Min-Li
;
Chen, Te-Yu
;
Chen, Yen-Chun
;
Chen, Yu-Chie
;
應用化學系
Various ionization methods in mass spectrometry (MS) are available for the analysis of analytes with different properties. Nonetheless, the use of a single ionization method to analyze mixtures containing analytes with different polarities and volatilities in different phases at atmospheric pressure remains a challenge. Exploring an ionization method that can ionize small organics and large biomolecules with different properties for MS analysis is advantageous. Carbon fiber ionization mass spectrometry (CFI-MS), which uses a carbon fiber bundle as the ion source, is useful for the analysis of small organics with low polarities. Voltage needs to be applied on the carbon fiber bundle to initiate corona discharge for ionization of analytes. In this study, we explore the suitability of using CFI-MS in the analysis of analytes in vapor, liquid, and solid phases using a single carbon fiber (length : similar to 1 cm; diameter: similar to 10 mu m) as the ion source. Furthermore direct electric contact on the carbon fiber is not required. We demonstrate that CFI-MS is useful for analyzing not only small and low-polarity organics but also polar biomolecules, such as peptides and proteins. The limits of detection for analytes with high polarities such as dodecyl trimethylammonium bromide and bradykinin are estimated to be similar to 16 and similar to 53 pM, respectively. Ionization mechanisms, including corona discharge and electrospray, are involved in the ionization of analytes with the polarity from low to high. Furthermore, sesame oil containing aromatic volatiles and compounds with different polarities is used as a model sample to demonstrate the capability of the developed ionization method to provide comprehensive chemical information from a complex sample. In addition, the feasibility of using the developed method for quantitative analysis of nonpolar as well as medium and high polarity analytes is also demonstrated. The sensitivity of the developed method toward analytes with high polarity is higher than those with low polarity. The method precision was estimated to be similar to 7.8%.
Carboxylate-functionalized iron oxide nanoparticles in surface-assisted laser desorption/ionization mass spectrometry for the analysis of small biomolecules
(2008)
Chiu, Yu-Chih
;
Chen, Yu-Chie
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Iron oxide particles have been demonstrated previously as an effective SALDI-assisted material in SALDI MS analysis. The addition of a proton source such as citrate salts is helpful for rendering ionization efficiency. To simplify the sample preparation steps, we immobilize polyacrylic acid (PAA) onto the surface of the iron oxide particles. The modified iron oxide particles can be used as the SALDI-assisted material without the addition of extra proton source. Small biomolecules including bradykinin, melittin, and insulin are used to examine the feasibility of this approach. The results show that the SALDI mass spectral results are improved by using polyacrylic acid (MWaverage= similar to 2 kDa) coated iron oxide nanoparticles.
Coffee-ring effects in laser desorption/ionization mass spectrometry
(2013-03-05)
Hu, Jie-Bi
;
Chen, Yu-Chie
;
Urban, Pawel L.
;
應用化學系
;
Department of Applied Chemistry
This report focuses on the heterogeneous distribution of small molecules (e.g. metabolites) within dry deposits of suspensions and solutions of inorganic and organic compounds with implications for chemical analysis of small molecules by laser desorption/ionization (LDI) mass spectrometry (MS). Taking advantage of the imaging capabilities of a modern mass spectrometer, we have investigated the occurrence of "coffee rings" in matrix-assisted laser desorption/ionization (MALDI) and surface-assisted laser desorption/ionization (SALDI) sample spots. It is seen that the "coffee-ring effect" in MALDI/SALDI samples can be both beneficial and disadvantageous. For example, formation of the coffee rings gives rise to heterogeneous distribution of analytes and matrices, thus compromising analytical performance and reproducibility of the mass spectrometric analysis. On the other hand, the coffee-ring effect can also be advantageous because it enables partial separation of analytes from some of the interfering molecules present in the sample. We report a "hidden coffee-ring effect" where under certain conditions the sample/matrix deposit appears relatively homogeneous when inspected by optical microscopy. Even in such cases, hidden coffee rings can still be found by implementing the MALDI-MS imaging technique. We have also found that to some extent, the coffee-ring effect can be suppressed during SALDI sample preparation. (C) 2013 Elsevier B.V. All rights reserved.