Fabrication of Nanostructured Mesoporous Germanium for Application in Laser Desorption Ionization Mass Spectrometry

Abstract

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is a high-throughput analytical technique ideally suited for small-molecule detection from different bodily fluids (e.g., saliva, urine, and blood plasma). Many SALDI-MS substrates require complex fabrication processes and further surface modifications. Furthermore, some substrates show instability upon exposure to ambient conditions and need to be kept under special inert conditions. We have successfully optimized mesoporous germanium (meso-pGe) using bipolar electrochemical etching and efficiently applied meso-pGe as a SALDI-MS substrate for the detection of illicit drugs such as in the context of workplace, roadside, and antiaddictive drug compliance. Argon plasma treatment improved the meso-pGe efficiency as a SALDI-MS substrate and eliminated the need for surface functionalization. The resulting substrate showed a precise surface geometry tuning by altering the etching parameters, and an outstanding performance for illicit drug detection with a limit of detection in Milli-Q water of 1.7 ng/mL and in spiked saliva as low as 5.3 ng/mL for cocaine. The meso-pGe substrate had a demonstrated stability over 56 days stored in ambient conditions. This proof-of-principle study demonstrates that meso-pGe can be reproducibly fabricated and applied as an analytical SALDI-MS substrate which opens the door for further analytical and forensic high-throughput applications.

Engineering Micro–Nanomaterials for Biomedical Translation

“…Semiconductor‐based nanomaterials have arguably become the most successful substrate of choice for SALDI–MS. pSi, [ 203 ] SiNWs, [ 204 ] and mesoporous germanium [ 205 ] have been used in MS studies due to their high UV absorption and thermal conductivity along with their functionalization capabilities to ensure tailor‐made analysis. Nanostructured‐silicon substrates have been explored in greater detail and emerged as the frontrunner for the SALDI–MS detection of low molecular weight drugs, [175b,206] metabolites, [ 207 ] and the profiling of biological fluids.…”

The ongoing evolution of laser desorption/ionization mass spectrometry: Some observations on current trends and future directions

“…A bewildering array of other matrix‐free LDI approaches have subsequently been reported including strategies based on zinc oxide, tungsten oxide, nanoporous materials, nanostructures (eg, nanowires, nanotubes, nanorods, and nanoparticles), and semiconductors (eg, germanium). Although these matrix‐free approaches vary in name and detail, they share two characteristics in common: First, they deliver low chemical noise and high sensitivity in the low‐mass range, and second, they all rely on interactions between the laser energy and the surfaces to transfer energy to analyte molecules and ionize them.…”

Morphology-Driven Control of Metabolite Selectivity Using Nanostructure-Initiator Mass Spectrometry

“…Surface morphology of NIMS substrates play an essential role in the desorption/ionization process of analyte molecules and thus determines the substrates’ sensitivity of transferring intact molecules into gas-phase ions. − As reported previously, NIMS signal is highly dependent on laser intensity, which suggests that efficient energy conversion happens during surface restructuring of NIMS substrates driving desorption/ionization. ,, However, the relationship between surface morphologies and NIMS performance toward different analytes is largely unexplored. Improved understanding on how NIMS surface morphology influences its sensitivity toward specific analytes has the potential to guide the developments of NIMS surfaces designed for increased metabolite coverage or potentially selective metabolite analysis. ,, …”