Elsevier

Analytica Chimica Acta

Volume 836, 11 July 2014, Pages 53-60
Analytica Chimica Acta

Top-down synthesized TiO2 nanowires as a solid matrix for surface-assisted laser desorption/ionization time-of-flight (SALDI-TOF) mass spectrometry

https://doi.org/10.1016/j.aca.2014.05.041Get rights and content

Highlights

  • TiO2 nanowires were synthesized as a solid matrix for SALDI-TOF MS by hydrothermal process.

  • The optimal crystal structure of TiO2 nanowires for SALDI-TOF MS were analyzed.

  • The feasibility TiO2 nanowires for SALDI-TOF MS was demonstrated for the analysis of amino acids and peptides.

Abstract

Top-down synthesized TiO2 nanowires are presented as an ideal solid matrix to analyze small biomolecules at a m/z of less than 500. The TiO2 nanowires were synthesized as arrays using a modified hydrothermal process directly on the surface of a Ti plate. Finally, the feasibility of the TiO2 nanowires in the anatase phase as a solid matrix. The crystal and electronic structures of the top-down TiO2 nanowires were analyzed at each step of the hydrothermal process, and the optimal TiO2 nanowires were identified by checking their performance toward the ionization of analytes in surface-assisted laser desorption/ionization time-of-flight (SALDI-TOF) mass spectrometry. Finally, the feasibility of the TiO2 nanowires in the anatase phase as a solid matrix for SALDI-TOF mass spectrometry was demonstrated using eight types of amino acids and peptides as model analytes.

Introduction

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry has been used as a powerful analytical tool for the analysis of biomolecules, such as peptides, proteins, and nucleic acids [1]. The advantages of MALDI-TOF mass spectrometry can be summarized by (1) the ease of sample preparation, (2) high sensitivity (<fM), and (3) a wide detection range (up to 300 kDa). In particular, MALDI-TOF mass spectrometry can ionize analytes without fragmentation of the analytes [2], [3]. However, this powerful tool has been restricted to the analysis of mass-to-charge ratios (m/z) higher than 500 because the matrix molecules are fragmented into irreproducible low-mass peaks. In this work, a target plate with top-down synthesized TiO2 nanowires is presented as an ideal solid matrix for the analysis of small biomolecules at a m/z of less than 500.

After Siuzdak and co-workers reported that porous silicon could be used as a solid matrix for the ionization of analytes in surface-assisted laser desorption/ionization time-of-flight (SALDI-TOF) mass spectrometry, various inorganic materials have been used as substitutes for the organic matrix for analytes at a m/z of less than 500 [4]. Nanomaterials, such as nanoparticles [5], [6], [7], carbon nanotubes [8], graphenes [9], and semiconductor nanowires [10], have been used as solid matrices in SALDI-TOF mass spectrometry. Although the exact ionization mechanism is not yet completely understood, the physical properties of nanomaterials related to energy absorption and transfer are supposed to strongly influence the ionization of analytes [11], [12]. In particular, TiO2 nanomaterials have been considered the most promising materials because of their strong absorption in the UV range, and TiO2 nanomaterials, such as thin films [13], [14], nanoparticles [15], and nanowires [10], have been reported as a solid matrix for SALDI-TOF mass spectrometry. The Ti-wire-based ionization method was also reported with probe electrospray ionization (PESI) mass spectrometry, which can be used to analyze small molecules without the influence of salts and detergents in the sample solution [16], [17], [18].

In this work, TiO2 nanowires were top-down synthesized on a solid matrix Ti plate for SALDI-TOF mass spectrometry through the hydrothermal process. The crystal and electronic structures of the top-down TiO2 nanowires were analyzed at each step of the hydrothermal process, and the optimal TiO2 nanowires were identified by checking their performance toward the ionization of analytes in SALDI-TOF mass spectrometry. Finally, the feasibility of the TiO2 nanowires in the anatase phase as a solid matrix for SALDI-TOF mass spectrometry was demonstrated using eight types of amino acids and peptides as model analytes.

Section snippets

Synthesis of TiO2 nanowire arrays

TiO2 nanowires were synthesized by the modified hydrothermal process [19], [20], [21], [22], [23], [24], [25]: (1) KOH treatment (TA), (2) water treatment (TAW) and (3) heat treatment (TAWH). Such top-down synthesized TiO2 nanowires can be prepared as arrays on a target plate using a parylene film as a protective layer against the highly corrosive etching conditions (10 M KOH) of the modified hydrothermal process, and the parylene film can be removed after the heat treatment step. As shown in

Properties of TiO2 nanowires prepared using the hydrothermal process

In this work, we focused on presenting the applicability of TiO2 nanowires prepared using the hydrothermal process to SALDI-TOF mass spectrometry. Usually, TiO2 nanowires are synthesized through the vapor–liquid–solid (VLS) mechanism using substrate materials in the gas phase under vacuum [[10], [11], [12]]. However, TiO2 nanowires from the hydrothermal process can be synthesized simply by changing aqueous solutions at ambient atmospheric conditions, as shown in Fig. 1(a). Therefore, the

Conclusions

In this work, top-down synthesized TiO2 nanowires were presented as a solid matrix for SALDI-TOF mass spectrometry. TiO2 nanowires were prepared on a Ti target plate as an array of 81 (9 × 9) nanowire zones with a diameter of 300 μm using the hydrothermal process and a protective parylene film. The feasibility of using TiO2 nanowires as a solid matrix for SALDI-TOF mass spectrometry was tested using peptides and amino acids as model analytes, and this method achieved a highly sensitive detection

Acknowledgements

This work was supported by DAPA and ADD. This research was also supported by the National Research Foundation of Korea (2009-0082188, 2013-056331 and 2013-056267).

References (47)

  • M. Müller et al.

    Limits for the detection of (poly-)phosphoinositides by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS)

    Chem. Phys. Lipids

    (2001)
  • D. Li et al.

    Origin of visible-light-driven photocatalysis: a comparative study on N/F-doped and N-F-codoped TiO2 powders by means of experimental characterizations and theoretical calculations

    J. Solid State Chem.

    (2005)
  • M. Zhang et al.

    Effect of annealing temperature on morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2

    J. Mol. Catal. A Chem.

    (2004)
  • X. Li et al.

    MALDI-TOF-MS analysis of small molecules using modified mesoporous material sba-15 as assisted matrix

    J. Am. Soc. Mass Spectrom.

    (2009)
  • G.L. Glish et al.

    The basics of mass spectrometry in the twenty-first century

    Nat. Rev. Drug Discov.

    (2003)
  • G.N. Schrauzer et al.

    Photocatalytic reactions. 1. Photolysis of water and photoreduction of nitrogen on titanium dioxide

    J. Am. Chem. Soc.

    (1977)
  • J. Wei et al.

    Desorption–ionization mass spectrometry on porous silicon

    Nature

    (1999)
  • M.J. Kang et al.

    Nanowire-assisted laser desorption and ionization mass spectrometry for quantitative analysis of small molecules

    Rapid Commun. Mass Spectrom.

    (2005)
  • S. Alimpiev et al.

    On the mechanism of laser induced desorption–ionization of organic compounds from etched silicon and carbon surfaces

    J. Chem. Phys.

    (2001)
  • R. Zenobi et al.

    Ion formation in MALDI mass spectrometry

    Mass Spectrom. Rev.

    (1998)
  • H. Sonderegger et al.

    Surface-assisted laser desorption/ionization-mass spectrometry using TiO2-coated steel targets for the analysis of small molecules

    Anal. Bioanal. Chem.

    (2011)
  • F. Torta et al.

    Titanium dioxide coated MALDI Plate for on target analysis of phosphopeptides

    J. Proteome. Res.

    (2009)
  • A.L. Castro et al.

    Titanium dioxide anatase as matrix for matrix-assisted laser desorption/ionization analysis of small molecules

    Rapid Commun. Mass Spectrom.

    (2008)
  • Cited by (31)

    • Recent advances in nanostructure/nanomaterial-assisted laser desorption/ionization mass spectrometry of low molecular mass compounds

      2019, Analytica Chimica Acta
      Citation Excerpt :

      After modified with cysteine, Au NPFs were used as an effective LDI medium with high efficiency and good reproducibility for small molecules and even low-molecular polymers. Using hydrothermal process, Pyun et al. [57] synthesized titanium dioxide (TiO2) NWs on the surface of titanium plate, and applied the surface as solid matrix for ionization of amino acids and small peptides. Later on, they simplified the synthesis procedure through wet-corrosion to prepare TiO2 NWs surface.

    • MoS<inf>2</inf>/Ag nanohybrid: A novel matrix with synergistic effect for small molecule drugs analysis by negative-ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

      2016, Analytica Chimica Acta
      Citation Excerpt :

      This technique is also known as surface-assisted laser desorption/ionization (SALDI) [6]. Up to now, a variety of inorganic nanomaterials with different compositions and morphologies, including silicon [7,8], metal/metal oxide [9–11], and carbon-based materials [12–14], have been utilized as MALDI matrices. These nanomaterial-based matrices minimized the background interferences, increased sensitivity, and simplified the sample preparation.

    • Analysis of benzylpenicillin in milk using MALDI-TOF mass spectrometry with top-down synthesized TiO<inf>2</inf> nanowires as the solid matrix

      2016, Chemosphere
      Citation Excerpt :

      The photocatalytic effect of TiO2 nanowires was reported to be observed with the anatase crystal structure, and the ionization of analyte was also reported to occur when using the anatase crystal structure. In particular, because of their strong absorption, TiO2 nanomaterials have been considered the most promising materials; thin films (Torta et al., 2009; Sonderegger et al., 2011), nanoparticles (Castro et al., 2008), and nanowires (Kim et al., 2014a) have been reported as the solid matrix for MALDI-TOF mass spectrometry. The Ti-wire-based ionization method was also reported with probe electrospray ionization (PESI) mass spectrometry, which can be used to analyze small molecules (Mandal et al., 2010).

    View all citing articles on Scopus
    View full text