Effects of Carbon Nanowalls (CNWs) Substrates on Soft Ionization of Low-Molecular-Weight Organic Compoundsin Surface-Assisted Laser Desorption/Ionization Mass Spectrometry (SALDI-MS)

Carbon nanowalls (CNWs), which are vertically oriented multi-layer graphene sheets, were employed in surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) measurements to detect low-molecular-weight organic compounds. CNWs substrates with widely different wall-to-wall distances from 142 to 467 nm were synthesized using a radical-injection plasma-enhanced chemical vapor deposition (RI-PECVD) system with nanosecond pulse biasing to a sample stage. When survival yield (SY) values of N-benzylpyridinium chloride (N-BP-Cl) were examined, which is commonly used to evaluate desorption/ionization efficiency, a narrower wall-to-wall distance presented a higher SY value. The highest SY value of 0.97 was realized at 4 mJ/cm² for the highest-density CNWs with a wall-to-wall distance of 142 nm. The laser desorption/ionization effect of arginine, an amino acid, was also investigated. When CNWs with a narrower wall-to-wall distance were used, the signal-to-noise (SN) ratios of the arginine signals were increased, while the intensity ratios of fragment ions to arginine signals were suppressed. Therefore, the CNWs nanostructures are a powerful tool when used as a SALDI substrate for the highly efficient desorption/ionization of low-molecular-weight biomolecules.

High-Performance Sample Substrate of Gold Nanoparticle Multilayers for Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

The development of a sample substrate with superior performance for desorption and ionization of analyte is the key issue to ameliorate the quality of mass spectra for measurements of small molecules in surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). Herein, the homogeneous sample substrate of gold nanoparticle multilayers (AuNPs-ML) with hexagonal lattice was successfully prepared by self-assembly technique. With strong surface plasmon resonance absorption and superior photothermal effect, the sample substrate of AuNPs-ML exhibited high signal sensitivity and low background noise for the detection of model analyte of glucose without additional matrixes in SALDI-MS. Furthermore, compared to merchant matrixes of α-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB), the sample substrate of AuNPs-ML was demonstrated to ameliorate the quality of mass spectra, including signal strength, background interference and signal/noise (S/N) ratio. The sucrose and tryptophan were also measured to show the extensive applications of AuNPs-ML sample substrate for the detections of small molecules in SALDI-MS. Most importantly, the remarkable reproducibility of glucose mass spectra with relative signal of 7.3% was obtained by the use of AuNPs-ML sample substrate for SALDI-MS. The homogeneous sample substrate of AuNPs-ML greatly improved the quality of mass spectra because of its strong absorption of laser energy, low specific heat, high heat conductivity and extraordinary homogeneity. We believe that AuNPs-ML could be a practical sample substrate for small molecule detection in SALDI-MS.

Atmospheric Pressure Plasma-Treated Carbon Nanowalls’ Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (CNW-SALDI-MS)

Carbon nanowalls (CNWs), vertically standing highly crystallizing graphene sheets, were used in the application of a surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS). The CNW substrates solved the issues on interferences of matrix molecules and alkali metal addition ions in low-weight molecule detection. Before SALDI sample preparations, the hydrophobic CNW was treated by atmospheric pressure plasma for exposing hydrophilicity to the CNWs’ surface. Detection of water soluble amino acids, arginine, was demonstrated.

Exploring the potential of electroless and electroplated noble metal-semiconductor hybrids within bio- and environmental sensing

Over the last two decades, the rapid development and widespread application of nanomaterials has significantly influenced research in various fields, including analytical chemistry and biosensing technologies. In particular, the simple functionalization and tuning of noble metal nanoparticle (NP) surface chemistry resulted in the development of a series of novel biosensing platforms with quick read-out and enhanced capabilities towards specific analyte detection. Moreover, noble metal NPs possess a number of unique properties, viz. high surface-to-volume ratio and excellent spectral, optical, thermal, electrical and catalytic characteristics. This manuscript provides an elaborate review on galvanic noble metal NPs deposited onto semiconductor surfaces, from the preparation stage towards their application in biosensors and gas sensing. Two types of deposition approaches, viz. galvanic displacement/electroless and conventional electroplating, are introduced and compared. Furthermore, the analytical merit of hybrid nanomaterials towards the improvement of sensing abilities is highlighted. Finally, some limitations and challenges related to progress in the development and application of analytical devices based on electroless and electroplated noble metal NPs-semiconductor hybrids (NMNPsHs) in biochemical and environmental sensing are discussed.

Small- and large-sized iron(II, III) oxide nanoparticles for surface-assisted laser desorption/ionization mass spectrometry of small biomolecules

RATIONALE

Common surface-assisted laser desorption/ionization (SALDI) surfaces are functionalized to improve mass spectrometric detection. Such surfaces are selective to certain group(s) of compounds. The application of universal and sensitive SALDI surfaces with appropriate size/surface area is paramount. In this study, two different sizes/surface areas of Fe3 O4 are compared as SALDI surfaces.

METHODS

For accurate surface area comparisons, the physical properties of the Fe3 O4 nanoparticles used as SALDI surfaces were determined using scanning electron microscopy, X-ray diffractometry, and N2 Brunauer-Emmet-Teller adsorption techniques. SALDI mass spectrometry (MS) data were acquired using a time-of-flight (TOF) mass spectrometer operated in the linear mode and equipped with a 50-Hz pulsed nitrogen laser (at 337 nm). Small biomolecules (adenosine, glucose, sucrose, tryptophan, and tripeptide) and a real sample (human serum) were analyzed.

RESULTS

The average sizes/specific surface areas of the SALDI surfaces of the small- and large-sized Fe3 O4 nanoparticles were ~21 nm/~82 m2 /g and ~39 nm/~38 m2 /g, respectively. An overall ~2.0-fold enhancement in signal-to-noise ratios was observed for the ionic species of the analyzed biomolecules in SALDI-MS using small-sized Fe3 O4 in comparison to large-sized Fe3 O4 nanoparticles. MS sensitivity from adenosine calibration curves (concentration between 0.05 and 10.0 mM) was ~2.0-fold higher for small-sized than large-sized Fe3 O4 nanoparticles as SALDI surfaces.

CONCLUSIONS

We have shown that transition-metal oxides such as Fe3 O4 nanoparticles are suitable and efficient surfaces for SALDI-TOF-MS analysis of small biomolecules. We observed improvement in signal-to-noise ratios and detection sensitivity for the analyzed samples from SALDI surfaces using small-sized (possessing larger surface area) than large-sized Fe3 O4 nanoparticles.

A novel laser desorption/ionization method using through hole porous alumina membranes

RATIONALE

A novel matrix-free laser desorption/ionization method based on porous alumina membranes was developed. The porous alumina membranes have a two-dimensional (2D) ordered structure consisting of closely aligned straight through holes of sub-micron in diameter that are amenable to mass production by industrial fabrication processes.

METHODS

Considering a balance between the ion generating efficiency and the mechanical strength of the membranes, the typical values for the hole diameter, open aperture ratio and membrane thickness were set to 200 nm, 50% and 5 μm, respectively. The membranes were coated with platinum on a single side that was exposed to the laser. Evaluation experiments were conducted on the feasibility of this membrane structure for an ionization method using a single peptide and mixed peptides and polyethylene glycol samples and a commercial matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometer in the positive ion mode.

RESULTS

Results showed a softness of ionization and no sweet spot nature. The capillary action of the through holes with very high aspect ratio enables several loading protocols including sample impregnation from the surface opposite to the laser exposure side.

CONCLUSIONS

The feasibility study indicates that the through hole porous alumina membranes have several advantages in terms of usefulness over the conventional surface-assisted laser desorption ionization (SALDI) methods. The proposed novel ionization method is termed Desorption Ionization Using Through Hole Alumina Membrane (DIUTHAME).

Tailored Interfaces of the Bulk Silicon Nanowire/TiO2 Heterojunction Promoting Enhanced Photovoltaic Performances

We report significantly improved silicon nanowire/TiO2 n+-n heterojunction solar cells prepared by sol-gel synthesis of TiO2 thin film atop vertically aligned silicon nanowire arrays obtained by facile metal-assisted wet electroless chemical etching of a bulk highly doped n-type silicon wafer. As we show here, chemical treatment of the nanowire arrays prior to depositing the sol-gel precursor has dramatic consequences on the device performance. While hydrofluoric treatment to remove the native oxide already improves significantly the device performances, hydrobromic (HBr) treatment consistently yields by far the best device performances with power conversion efficiencies ranging between 4.2 and 6.2% with fill factors up to 60% under AM 1.5G illumination. In addition to yield high-quality and easy to produce solar cell devices, these findings regarding the surface treatment of silicon nanowires with HBr suggest that HBr could contribute to the enhancement of the device performance not only for solar cells but also for other optoelectronics devices based on semiconductor nanostructures.

Exploring the Efficacy of Platinum and Palladium Nanostructures for Organic Molecule Detection via Raman Spectroscopy

Noble transition metals, like palladium (Pd) and platinum (Pt), have been well-known for their excellent catalytic and electrochemical properties. However, they have been considered non-active for surface enhanced Raman spectroscopy (SERS). In this work, we explore the scattering contributions of Pd and Pt for the detection of organic molecules. The Pd and Pt nanostructures were synthesized on silicon substrate using a modified galvanic displacement method. The results show Pt nanoparticles and dendritic Pd nanostructures with controlled density and size. The influence of surfactants, including sodium dodecyl sulfate and cetyltrimethylammonium bromide, on the size and morphology of the nanostructures was investigated. The Pd and Pt nanostructures with a combination of large size and high density were then used to explore their applicability for the detection of 10⁻⁵ M Rhodamine 6G and 10⁻² M paraoxon.

Combined analysis of 1,3-benzodioxoles by crystalline sponge X-ray crystallography and laser desorption ionization mass spectrometry

The combination of X-ray analysis and laser desorption ionization by using crystalline sponge will be a promising method to determine guest structures.

Mechanisms of Nanophase-Induced Desorption in LDI-MS. A Short Review

Nanomaterials are frequently used in laser desorption ionization mass spectrometry (LDI-MS) as DI enhancers, providing excellent figures of merit for the analysis of low molecular weight organic molecules. In recent years, literature on this topic has benefited from several studies assessing the fundamental aspects of the ion desorption efficiency and the internal energy transfer, in the case of model analytes. Several different parameters have been investigated, including the intrinsic chemical and physical properties of the nanophase (chemical composition, thermal conductivity, photo-absorption efficiency, specific heat capacity, phase transition point, explosion threshold, etc.), along with morphological parameters such as the nanophase size, shape, and interparticle distance. Other aspects, such as the composition, roughness and defects of the substrate supporting the LDI-active nanophases, the nanophase binding affinity towards the target analyte, the role of water molecules, have been taken into account as well. Readers interested in nanoparticle based LDI-MS sub-techniques (SALDI-, SELDI-, NALDI- MS) will find here a concise overview of the recent findings in the specialized field of fundamental and mechanistic studies, shading light on the desorption ionization phenomena responsible of the outperforming MS data offered by these techniques.

Counter electrodes in dye-sensitized solar cells

This article panoramically reviews the counter electrodes in dye-sensitized solar cells, which is of great significance for the development of photovoltaic and photoelectric devices.

A study of enhanced ion formation from metal-semiconductor complexes in atmospheric pressure laser desorption/ionization mass spectrometry

The study of the key parameters impacted surface-assisted laser desorption/ionization-mass spectrometry is of broad interest. In previous studies, it has been shown that surface-assisted laser desorption/ionization-mass spectrometry is a complex process depending on multiple factors. In the presented study, we showed that neither porosity, light absorbance nor surface hydrophobicity alone influence the enhancement phenomena observed from the hybrid metal-semiconductor complexes versus individual targets, but small changes in the analyte attaching to the target significantly affect laser desorption ionization-efficiency. By means of Raman spectroscopy and scanning electron microscopy, it was revealed that the formation of an amorphous analyte layer after drying on a solid substrate was essential for the enhanced laser desorption ionization-signal observed from the hybrid metal-semiconductor targets, and the crystallization properties of the analyte appeared as a function of the substrate. Obtained results were used for the screening of regular and lactose-free milk samples through the hybrid metal-semiconductor target. Copyright © 2016 John Wiley & Sons, Ltd.

Functionalization of silicon nanowire arrays by silver nanoparticles for the laser desorption ionization mass spectrometry analysis of vegetable oils

In this work, novel hybrid nanostructured surfaces, consisting of dense arrays of silicon nanowires (SiNWs) functionalized by Ag nanoparticles (AgNP/SiNWs), were used for the laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) analysis of some typical unsaturated food components (e.g. squalene, oleic acid) to assess their MS performance. The synthesis of the novel platforms is an easy, cost-effective process based on the maskless wet-etching preparation at room temperature of SiNWs followed by their decoration with AgNPs, produced by pulsed laser deposition. No particular surface pretreatment or addition of organic matrixes/ionizers was necessary. Moreover, oil extracts (e.g. extra virgin olive oil, peanut oil) could be investigated on AgNP/SiNWs surfaces, revealing their different MS profiles. It was shown that such substrates operate at reduced laser energy, typically generating intense silver cluster ions and analyte adducts. A comparison with bare SiNWs was also performed, indicating the importance of AgNP density on NW surface. In this case, desorption/ionization on silicon was invoked as probable LDI mechanism. Finally, the influence of SiNW length and surface composition on MS results was assessed. The combination of typical properties of SiNWs (hydrophobicity, antireflectivity) with ionization ability of metal NPs can be a valid methodology for the further development of nanostructured surfaces in LDI-TOF MS applications. Copyright © 2016 John Wiley & Sons, Ltd.

Identification of Microalgae by Laser Desorption/Ionization Mass Spectrometry Coupled with Multiple Nanomatrices

In this study, we demonstrate a simple method to identify microalgae by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using three different substrates: HgSe, HgTe, and HgTeSe nanostructures. The fragmentation/ionization processes of complex molecules in algae varied according to the heat absorption and transfer efficiency of the nanostructured matrices (NMs). Therefore, the mass spectra obtained for microalgae showed different patterns of m/z values for different NMs. The spectra contained both significant and nonsignificant peaks. Constructing a Venn diagram with the significant peaks obtained for algae when using HgSe, HgTe, and HgTeSe NMs in m/z ratio range 100-1000, a unique relationship among the three sets of values was obtained. This unique relationship of sets is different for each species of microalgae. Therefore, by observing the particular relationship of sets, we successfully identified different algae such as Isochrysis galbana, Emiliania huxleyi, Thalassiosira weissflogii, Nannochloris sp., Skeletonema cf. costatum, and Tetraselmis chui. This simple and cost-effective SALDI-MS analysis method coupled with multi-nanomaterials as substrates may be extended to identify other microalgae and microorganisms in real samples. Graphical Abstract Identification of microalgae by surface-assisted laser desorption/ionization mass spectrometry coupled with three different mercury-based nanosubstrates.

Facile synthesis of gold@graphitized mesoporous silica nanocomposite and its surface-assisted laser desorption/ionization for time-of-flight mass spectroscopy

In this work, a novel core-shell structured gold@graphitized mesoporous silica nanocomposite (Au@GMSN) was synthesized by in situ graphitization of template within the mesochannels of mesoporous silica shell on gold core and demonstrated to be promising nanomaterials for surface-assisted laser desorption/ionization time-of-flight mass spectroscopy (SALDI-TOF MS). The integration of the graphitized mesoporous silica with the gold nanoparticles endowed Au@GMSN with large surface areas of graphitic structure, good dispersibility, and strong ultraviolet (UV) absorption. Au@GMSN exerted the synergistic effect on the efficient detection of small-molecular-weight analytes including amino acids, neutral saccharides, peptides, and traditional Chinese medicine. The Au@GMSN-assisted laser desorption/ionization exhibited the following superiorities: high ionization efficiency, low fragmentation interference, favorable salt tolerance, and good reproducibility. Moreover, because of the large hydrophobic inner surface area of the graphitized mesoporous silica shell, the Au@GMSN demonstrated its promising capacity in the pre-enrichment of aromatic analytes prior to SALDI-TOF MS, which favored rapid and sensitive detection.

Laser desorption ionization (LDI) silicon nanopost array chips fabricated using deep UV projection lithography and deep reactive ion etching

A nanofabricated laser desorption ionization mass spectrometry (LDI-MS) chip for quantitation of small molecules.

The role of physical and chemical properties of Pd nanostructured materials immobilized on inorganic carriers on ion formation in atmospheric pressure laser desorption/ionization mass spectrometry

Fundamental parameters influencing the ion-producing efficiency of palladium nanostructures (nanoparticles [Pd-NP], nanoflowers, nanofilms) during laser irradiation were studied in this paper. The nanostructures were immobilized on the surface of different solid inorganic carrier materials (porous and mono-crystalline silicon, anodic porous aluminum oxide, glass and polished steel) by using classical galvanic deposition, electroless local deposition and sputtering. It was the goal of this study to investigate the influence of both the nanoparticular layer as well as the carrier material on ion production for selected analyte molecules. Our experiments demonstrated that the dimensions of the synthesized nanostructures, the thickness of the active layers, surface disorders, thermal conductivity and physically or chemically adsorbed water influenced signal intensities of analyte ions during surface-assisted laser desorption/ionization (SALDI) while no effects such as plasmon resonance, photoelectric effect or catalytic activity were expected to occur. Excellent LDI abilities were seen for Pd-NPs immobilized on steel, while Pd nanoflowers on porous silicon exhibited several disadvantages; viz, strong memory effects, dependency of the analytical signal on amount of physically and chemically adsorbed water inside porous carrier, reduced SALDI activity from unstable connections between Pd and semiconductor material, decrease of the melting point of pure silicon after Pd immobilization and resulting strong laser ablation of metal/semiconductor complex, as well as significantly changed surface morphology after laser irradiation. The analytical performance of Pd-NP/steel was further improved by applying a hydrophobic coating to the steel surface before galvanic deposition. This procedure increased the distance between Pd-NPs, thus reducing thermal stress upon LDI; it simultaneously decreased spot sizes of deposited sample solutions.

Novel galvanic nanostructures of Ag and Pd for efficient laser desorption/ionization of low molecular weight compounds

A simple approach for synthesis of palladium and silver nanostructures with readily adjustable morphologies was developed using galvanic electrochemical deposition, for application to surface-assisted laser desorption/ionization (SALDI) of small biological molecules. A range of fatty acids, triglycerides, carbohydrates, and antibiotics were investigated to assess the performance of the new materials. Intense analyte cations were generated from the galvanic surfaces upon UV laser irradiation such as potassium adducts for a film thickness <100 nm (originating from impurities of the electrolyte solution) and Pd and Ag cluster ions for films with a thickness >120 nm. Possible laser desorption/ionization mechanisms of these galvanic structures are discussed. The films exhibited self-organizing abilities and adjustable morphologies by changing electrochemical parameters. They did not require any stabilizing agents and were inexpensive and very easy to produce. SALDI analysis showed that the materials were stable under ambient conditions and analytical results with excellent measurement reproducibility and detection sensitivity similar to MALDI were obtained. Finally, we applied the galvanic surfaces to fast screening of natural oils with minimum sample preparation.

Pulsed-laser desorption/ionization of clusters from biofunctional gold nanoparticles: implications for protein detections

In this paper, we describe a pulsed-laser desorption/ionization mass spectrometry (LDI-MS) approach for the detection of proteins with femtomolar sensitivity through the analysis of gold (Au) clusters desorbed from aptamer-modified gold nanoparticles (Apt-AuNPs) on a nitrocellulose membrane (NCM). After the target protein (thrombin) was selectively captured by the surface-bound 29-mer thrombin-binding aptamer (TBA(29)), the thrombin/TBA(29)-AuNP complexes were concentrated and deposited onto the NCM to form a highly efficient background-free surface-assisted LDI substrate. Under pulsed laser irradiation (355 nm), the binding of thrombin decreased the desorption and/or ionization efficiencies of the Au atoms from the AuNP surfaces. The resulting decreases in the intensities of the signals for Au clusters in the mass spectra provided a highly amplified target-labeling indicator for the targeted protein. Under optimized conditions, this probe was highly sensitive (limit of detection: ca. 50 fM) and selective (by at least 1000-fold over other proteins) toward thrombin; it also improved reproducibility (<5%) of ion production by presenting a more-homogeneous substrate surface, thereby enabling LDI-based measurements for the accurate and precise quantification of thrombin in human serum. This novel LDI-MS approach allows high-speed analyses of low-abundance thrombin with ultrahigh sensitivity; decorating the AuNP surfaces with other aptamers also allowed amplification of other biological signals.

Functionalized graphene-coated cobalt nanoparticles for highly efficient surface-assisted laser desorption/ionization mass spectrometry analysis

Graphene-coated cobalt nanoparticles surface-functionalized with benzylamine groups (CoC-NH(2) nanomagnets) were shown to effectively enrich analytes for surface-assisted laser desorption/ionization mass spectrometry (affinity SALDI-MS) analysis. These CoC-NH(2) nanomagnets are highly suited for use with affinity SALDI-MS because their mean diameter of 30 nm, high specific surface area of 15 m(2) g(-1), and high-strength saturation magnetization of 158 emu g(-1) led to efficient extraction of analytes by magnetic separation, which in turn enabled excellent SALDI-MS performance. Surface modification of CoC nanomagnets with benzylamine groups increased the yield of peptide ions and decreased fragmentation of benzylpyridinium ions, so-called "thermometer ions" formed through soft ionization. The CoC-NH(2) nanomagnets were used to extract perfluorooctanesulfonate from large volumes of aqueous solutions by magnetic separation, which was identified directly by SALDI-MS analysis with high sensitivity even at the sub-part-per-trillion level (∼0.1 ng/L). The applicability of CoC-NH(2) nanomagnets in conjunction with SALDI-MS for the enrichment and detection of pentachlorophenol, bisphenol A, and polyfluorinated compounds (PFCs) with varying chain length, which are environmentally significant compounds, as well as small drugs, was also evaluated.

Simple pretreatment of non-conductive small hydrous bio-samples with choline-type ionic liquid and membrane filter for microsample mounting

Choline-type ionic liquids (CILs), which have a molecular structure resembling that of the vitamin-like active substance choline, have high water solubility, high osmotic pressure, and high cell membrane permeability. Their physical properties make them a very useful pretreatment agent for scanning electron microscopy (SEM) observation of hydrous samples because they can replace water in the samples, causing them to retain their shapes. SEM images of pollen without dissolution of cell membranes, damage, or deformation were obtained by a simple visualization process using CILs. We also identified an easy pretreatment protocol for SEM observation of hydrous microsamples that uses a membrane filter as a sample stage to ensure correct sample placement. Bacteria were successfully observed by using this protocol.

Flower-like Na2O nanotip synthesis via femtosecond laser ablation of glass

The current state-of-the-art in nanotip synthesis relies on techniques that utilize elaborate precursor chemicals, catalysts, or vacuum conditions, and any combination thereof. To realize their ultimate potential, synthesized nanotips require simpler fabrication techniques that allow for control over their final nano-morphology. We present a unique, dry, catalyst-free, and ambient condition method for creating densely clustered, flower-like, sodium oxide (Na2O) nanotips with controllable tip widths. Femtosecond laser ablation of a soda-lime glass substrate at a megahertz repetition rate, with nitrogen flow, was employed to generate nanotips with base and head widths as small as 100 and 20 nm respectively, and lengths as long as 10 μm. Control of the nanotip widths was demonstrated via laser dwell time with longer dwell times producing denser clusters of thinner nanotips. Energy dispersive X-ray analysis reveals that nanotip composition is Na2O. A new formation mechanism is proposed, involving an electrostatic effect between ionized nitrogen and polar Na2O. The synthesized nanotips may potentially be used in antibacterial and hydrogen storage applications.

Oligonucleotide analysis by nanoparticle-assisted laser desorption/ionization mass spectrometry

We analyzed oligonucleotides by nanoparticle-assisted laser desorption/ionization (nano-PALDI) mass spectrometry (MS). To this end, we prepared several kinds of nanoparticles (Cr-, Fe-, Mn-, Co-based) and optimized the nano-PALDI MS method to analyze the oligonucleotides. Iron oxide nanoparticles with diammonium hydrogen citrate were found to serve as an effective ionization-assisting reagent in MS. The mass spectra showed both [M - H](-) and [M + xMe(2+)- H](-) (Me: transition metal) peaks. The number of metal-adducted ion signals depended on the length of the oligonucleotide. This phenomenon was only observed using bivalent metal core nanoparticles, not with any other valency metal core nanoparticles. Our pilot study demonstrated that iron oxide nanoparticles could easily ionize samples such as chemical drugs and peptides as well as oligonucleotides without the aid of an oligonucleotide-specific chemical matrix (e.g., 3-hydroxypicolinic acid) used in conventional MS methods. These results suggested that iron-based nanoparticles may serve as the assisting material of ionization for genes and other biomolecules.

Steroid hormones analysis with surface-assisted laser desorption/ionization mass spectrometry using catechin-modified titanium dioxide nanoparticles

This paper describes the application of catechin-modified titanium dioxide nanoparticles (TiO(2) NPs) as matrices to analyze four steroid hormones by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The catechin-modified TiO(2) NPs have high absorbance at 337 nm and are effective SALDI matrices when using a nitrogen laser. Four test steroid hormones-cortisone, hydrocortisone, progesterone, and testosterone-were directly analyzed by SALDI-MS. The limits of detection at a signal-to-noise ratio of 3 for cortisone, hydrocortisone, progesterone, and testosterone were 1.62, 0.70, 0.66, and 0.23 μM, respectively. This approach provides good quantitative linearity for the four analytes (R(2)>0.986) with good reproducibility (the shot-to-shot and batch-to-batch variations for the four analytes were less than 10% and 15%, respectively). We validated the practicality of this approach-considering its advantages in sensitivity, repeatability, rapidity, and simplicity-through the analysis of testosterone in a urine sample.