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

AuNPs/CNC Nanocomposite with A "Dual Dispersion" Effect for LDI-TOF MS Analysis of Intact Proteins in NSCLC Serum Exosomes

Detecting exosomal markers using laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) is a novel approach for examining liquid biopsies of non-small cell lung cancer (NSCLC) samples. However, LDI-TOF MS is limited by low sensitivity and poor reproducibility when analyzing intact proteins directly. In this report, gold nanoparticles/cellulose nanocrystals (AuNPs/CNC) is introduced as the matrix for direct analysis of intact proteins in NSCLC serum exosomes. AuNPs/CNC with "dual dispersion" effects dispersed and stabilized AuNPs and improved ion inhibition effects caused by protein aggregation. These features increased the signal-to-noise ratio of [M+H]+ peaks by two orders of magnitude and lowered the detection limit of intact proteins to 0.01 mg mL-1. The coefficient of variation with or without AuNPs/CNC is measured as 10.2% and 32.5%, respectively. The excellent reproducibility yielded a linear relationship (y = 15.41x - 7.983, R2 = 0.989) over the protein concentration range of 0.01 to 20 mg mL-1. Finally, AuNPs/CNC-assisted LDI-TOF MS provides clinically relevant fingerprint information of exosomal proteins in NSCLC serum, and characteristic proteins S100 calcium-binding protein A10, Urokinase plasminogen activator surface receptor, Plasma protease C1 inhibitor, Tyrosine-protein kinase Fgr and Mannose-binding lectin associated serine protease 2 represented excellent predictive biomarkers of NSCLC risk.

Gold-Silver and Gold-Palladium Alloy Nanoparticles as Mass-Probes for Immunosensing

Silver or palladium shelled gold nanoparticles were fused into alloy nanoparticles by pulsed-laser irradiation. The alloy nanoparticles could carry antibodies on their surfaces without affecting their immune functionalities and interact selectively with antigens on a blotting membrane. Silver or palladium ions desorbed from the alloy nanoparticles as reporter ions upon the UV laser irradiation in a mass spectrometer.

Engineering of nanomaterials for mass spectrometry analysis of biomolecules

Mass spectrometry (MS) based analysis has received intense attention in diverse biological fields. However, direct MS interrogation of target biomolecules in complex biological samples is still challenging, due to the extremely low abundance and poor ionization potency of target biological species. Innovations in nanomaterials create new auxiliary tools for deep and comprehensive MS characterization of biomolecules. More recently, growing research interest has been directed to the compositional and structural engineering of nanomaterials for enriching target biomolecules prior to MS analysis, enhancing the ionization efficiency in MS detection and designing biosensing nanoprobes in sensitive MS readout. In this review, we mainly focus on the recent advances in the engineering of nanomaterials towards their applications in sample pre-treatment, desorption/ionization matrices and ion signal amplification for MS profiling of biomolecules. This review will provide a toolbox of nanomaterials for researchers devoted to developing analytical methods and practical applications in the biological MS field.

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.

Monitoring thrombin generation and screening anticoagulants through pulse laser-induced fragmentation of biofunctional nanogold on cellulose membranes

Thrombin generation (TG) has an important part in the blood coagulation system, and monitoring TG is useful for diagnosing various health issues related to hypo-coagulability and hyper-coagulability. In this study, we constructed probes by using mixed cellulose ester membranes (MCEMs) modified with gold nanoparticles (Au NPs) for monitoring thrombin activity using laser desorption/ionization mass spectrometry (LDI-MS). The LDI process produced Au cationic clusters ([Au(n)](+); n = 1-3) that we detected through MS. When thrombin reacted with fibrinogen on the Au NPs-MCEMs, insoluble fibrin was formed, hindering the formation of Au cationic clusters and, thereby, decreasing the intensity of their signals in the mass spectrum. Accordingly, we incorporated fibrinogen onto the Au NPs-MCEMs to form Fib-Au NPs-MCEM probes to monitor TG with good selectivity (>1000-fold toward thrombin with respect to other proteins or enzymes) and sensitivity (limit of detection for thrombin of ca. 2.5 pM in human plasma samples). Our probe exhibited remarkable performance in monitoring the inhibition of thrombin activity by direct thrombin inhibitors. Analyses of real samples using our new membrane-based probe suggested that it will be highly useful in practical applications for the effective management of hemostatic complications.

Colorimetric determination of DNA methylation based on the strength of the hydrophobic interactions between DNA and gold nanoparticles

A simple, novel colorimetric nanosensor for DNA methylation based on the strength of hydrophobic interaction between DNA and gold nanoparticles was proposed. The nanosensing of oligonucleotides with four nitrogen bases was first demonstrated by dividing the bases into two groups (A/T and C/G) using the representative colors that correspond to Watson-Crick base pairing. By treatment of the genomic DNA with sodium bisulfite followed by PCR amplification, the methylation level of nasopharyngeal carcinoma cells treated with 5-aza-2'-deoxycytidine for up to 5 days could be discriminated by naked eye observation. Furthermore, 12 cancer cell lines that demonstrate heterogeneity with respect to DNA methylation could also be distinguished using the nanosensor, even for amplicons as long as 342 bp. These results demonstrate that the proposed colorimetric nanosensor could potentially be useful in epigenetic studies.

Gold-nanoparticles-modified cellulose membrane coupled with laser desorption/ionization mass spectrometry for detection of iodide in urine

We report an efficient method for the determination of iodide (I(-)) ions by using gold-iodide hybrid cluster ions on gold nanoparticles (Au NPs) modified mixed cellulose ester membrane (Au NPs-MCEM) by pulsed laser desorption/ionization mass spectrometry (LDI-MS). When I(-) ions were deposited and concentrated on the surfaces of Au NPs (32 nm) via strong Au(+)-I(-) interaction on the MECM, the Au NPs-MCEM was observed to function as an efficient surface-assisted LDI substrate with very low background noise. When pulsed laser radiation (355 nm) was applied, I(-) binding to Au NPs ions induced the enhancement of the desorption and ionization efficiency of gold-iodide hybrid cluster ions from the Au NPs surfaces. The reproducibility of the probe for both shot-to-shot and sample-to-sample (both less than 10%) ion production was also improved by the homogeneous nature of the substrate surface. Thus, it allows the accurate and precise quantification of I(-) ions in high-salinity real samples (i.e., edible salt samples and urine) at the nanomolar range. This novel LDI-MS approach provides a simple route for the high-speed analysis of I(-) ions with high sensitivity and selectivity in real biological samples.