A MALDI-MS-based impact assessment of ZnO nanoparticles, nanorods and quantum dots on the lipid profile of bacterial pathogens.

MALDI-MS was used for studying the impact of zinc oxide (ZnO) nanomaterials on Pseudomonas aeruginosa and Staphylococcus aureus. The growth patterns of both these bacterial pathogens in the presence of the ZnO nanomaterials and the subsequent lipidomic changes were assessed using an optimized simple, rapid MALDI-MS based methodology. All three nanostructures tested exhibited differential bactericidal activity unique to P. aeruginosa and S. aureus. The results indicated that the ZnO nanomaterials were highly inhibitory to S. aureus even at 70 mg L-1, while in the case of P. aeruginosa, the ZnO nanomaterials were compatible for up to 10 h and beyond 10 h only marginal growth inhibition was observed. The results proved that the shapes of the ZnO nanomaterials did not affect their toxicity properties. MALDI-MS was applied to study the lipidomic changes of P. aeruginosa and S. aureus after nanomaterial treatment, in order to throw light on the mechanism of growth inhibition. The results from the MALDI-MS studies showed that the ZnO nanostructures exhibited only marginal changes in the lipidomic profile both in the case of P. aeruginosa and S. aureus. These preliminary results indicate that the mechanism of growth inhibition by the ZnO nanomaterial is not through lipid-based interactions, but apparently more so via protein inhibitions.

Graphene nanosheet mediated MALDI-MS (GN-MALDI-MS) for rapid, in situ detection of intact incipient biofilm on material surfaces.

Detection is the first step to efficient treatment, therefore early detection of biofilm gains paramount importance for the initiation of mitigation protocols. A systematic study was conducted to detect the biofilm formation (1h to 2month period) on aluminium, titanium surfaces and their corresponding oxide film surfaces. The limit of detection (LOD) in case of traditional MALDI-MS was limited to a 6h old biofilm. Whereas, in case of the Graphene nanosheet mediated MALDI-MS (GN-MALDI-MS) approach, early detection of the biofilm was demonstrated to be 1h on titanium surfaces and 3h for Al surfaces.

Graphene nanoflakes as an efficient ionizing matrix for MALDI-MS based lipidomics of cancer cells and cancer stem cells.

This study demonstrates that graphene nanoflakes can be efficiently used as a successful, interference free matrix for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The method is referred to as graphene-assisted laser desorption/ionization mass spectrometry (GALDI-MS), and it can be used for lipidomic analysis of cancer cells and cancer stem cells. The graphene nanoflakes were synthesized in-house and exhibited a transparent flake-like shape with characteristic crumpled silk waves in transmission electron microscopy and typical absorption characteristics upon UV-vis (λmax = 270 nm) and Fourier-transform infrared spectroscopic analysis. Graphene nanoflakes were tested as a sole matrix and co-matrix with traditional MALDI-MS matrices for the lipid extracts obtained from normal breast, cancer and cancer stem cells with four different spotting methods. In all the cases, the graphene nanoflakes displayed a noise free and good quality mass spectrum. This study reveals the possibility that lipids could self-assemble as a multi-layered structure on the graphene nanoflake platform by electrostatic interactions between the graphene nanoflakes and the lipid head groups and thus result in noise-free spectra from GALDI-MS based lipidomics.

Chitosan nanomagnets for effective extraction and sensitive mass spectrometric detection of pathogenic bacterial endotoxin from human urine.

Direct analysis and profiling of a complex endotoxin without any prior purification or sample treatment techniques using chitosan nanomagnets coupled with MALDI-MS techniques has been demonstrated. Surface modified magnetic nanoparticles such as Fe3O4 and CuFeO2 with chitosan were synthesized and characterized by using UV, TEM, and FTIR. Endotoxin (lipopolysaccharides (LPS)) was spiked into human urine and recovery enabled using chitosan nanomagnets. For the first time, the use of CuFeO2@chitosan and Fe3O4@chitosan nanomagnets for affinity based separation and enrichment of trace levels of endotoxin and direct detection using MALDI-MS has been successfully achieved. The chitosan nanomagnet based recovery of endotoxin from urine samples showed a high degree of sensitivity compared to the conventional MALDI-MS analysis, where the lowest detectable endotoxin concentration was 30 mg mL-1 (0.15 mg, 5 µL). The Fe3O4@chitosan nanomagnet approach has 67 times higher sensitivity at 450 µg mL-1 (2.25 µg, 5 µL) compared to the direct MALDI-MS analysis. However, CuFeO2@chitosan nanomagnets appeared to be more effective than Fe3O4@chitosan nanomagnets (about 4 times) and 250 times more sensitive for separation at 120 µg mL-1 (0.6 µg, 5 µL) and detection of endotoxin from urine. The current approach proposes a novel MALDI-MS platform using the chitosan nanomagnets for extraction/detection of endotoxin from clinical samples such as human urine which can be further applied for biomedicine/clinical application for rapid, sensitive, direct and effective detection for bacterial infections.