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

Pulsed laser irradiation induces the generation of alloy cluster ions for the screening of protease activity

Pulsed laser irradiation can cause the fragmentation of nanoparticles, which generates cluster ions. This allows nanoparticles to be adopted as mass tag/signal amplifiers in laser desorption/ionization mass spectrometry (LDI-MS) bioassays. Herein, we demonstrate the potential of using the signal from alloy cluster ions in bioassays through a fibrin clot model to determine the activity of thrombin. A mixed solution of silver and gold nanoparticles functionalized with fibrinogen (Fg‒Ag NPs/Fg‒Au NPs) treated with thrombin can form clots composed of aggregated fibrin-Au NPs/Ag NPs. These clots analyzed with LDI-MS are noted to form intense Ag-Au alloy cluster ions, especially [Ag₂Au]⁺, which were used to detect thrombin concentration with a dynamic range of 2.5-50 pM in human plasma. This sensing platform was further employed for the screening of direct thrombin inhibitors. This work developed a novel bioassay utilizing metallic gas-phase reactions generated from pulsed laser irradiation of aggregated nanoparticles to monitor enzymatic activity and to screen inhibitors. We believe that LDS-MS can serve as a new platform for gas-phase reaction-based bioassays.

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.

Nanoparticle-Based LDI-MS Immunoassay for the Multiple Diagnosis of Viral Infections

Many serious public health emergencies around the globe are caused by viral epidemics. Thus, developing a reliable method for viral screening is in high demand. Multiplex assays for simultaneous detection and fast screening of high-risk pathogens are especially needed. This study employs metal nanoparticles to generate specific mass spectral signals for different RNA viruses, which enables simultaneous detection of whole viruses by laser desorption/ionization mass spectrometry (LDI-MS). We developed a nanoparticle-based sandwich immunosorbent assay as a sensing platform for the detection of viruses and viral nonstructural protein by LDI-MS. Cellulose acetate membrane (CAM) serves as the substrate for the fabrication of the sandwich immunosorbent assay with the advantages of clean mass spectra and high enrichment of analytes. Antibody-modified metal nanoparticles (Ab-MNPs; M = Au or Ag) act as metallic biocodes for the LDI-MS detection. The signal amplification readout for the virus is through the pulsed laser-induced formation of metal cluster ions ([M _n]⁺; n = 1-3) from the Ab-MNPs which specifically bind on the CAM. Our sensing system is effective for the detection of intact viruses [Enterovirus 71 (EV71) and Japanese encephalitis virus (JEV)], nonstructural protein 1 (NS1) of Zika virus (ZIKV), EV71-spiked human serum samples, and the simultaneous detection of EV71 and ZIKV. Our probe efficiently detects EV71 in real clinical serum samples with >95% agreement with RT-qPCR results. This high-throughput LDI-MS viral detection system is simple, reliable, and high-throughput. We believe this platform has the potential to be employed for the routine screening of patients with viral infections.

Inhibition of catalytic activity of fibrinogen-stabilized gold nanoparticles via thrombin-induced inclusion of nanoparticle into fibrin: Application for thrombin sensing with more than 104-fold selectivity

Citrate-capped gold nanoparticles (AuNPs) modified with thrombin-binding aptamer are often implemented for colorimetric, fluorescent, and electrochemical detection of thrombin in an aqueous solution. However, researchers have rarely explored the application of fibrinogen-modified AuNPs (F-AuNPs) for thrombin sensing. We present a simple, inexpensive, sensitive, and selective probe for colorimetric assay of thrombin through combining thrombin-induced inclusion of F-AuNPs into Fibrin and F-AuNPs-catalyzed reduction of 4-nitrophenol with an excess amount of NaBH₄. Considering that fibrinogen stabilized citrate-capped AuNPs against a high-ionic-strength buffer, F-AuNPs efficiently catalyzed the NaBH₄-mediated decrease of yellow 4-nitrophenol to colorless 4-aminophenol. The presence of thrombin converted fibrinogen into fibrin on the nanoparticle surface, leading to the inclusion of nanoparticles into fibrin. The formation of fibrin inhibited that the AuNPs catalyzed the NaBH₄-mediated reduction of 4-nitrophenol. Consequently, the color of the solution gradually varied from colorless to yellow with increasing thrombin concentration. The proposed system was shown to be accurate in the quantification of small differences in the concentration of human thrombin over the range of 4-60 pM. The lowest detectable concentration of human thrombin by the naked eye was as low as 16 pM. We demonstrated the practical application of the proposed system in quantifying 1-15 nM human thrombin in human plasma.

Satellite-like Gold Nanocomposites for Targeted Mass Spectrometry Imaging of Tumor Tissues

We have developed a simple, rapid, high-throughput cancer diagnosis system using functional nanoparticles (NPs) consisting of poly(catechin) capped-gold NPs (Au@PC NPs) and smaller nucleolin-binding aptamer (AS1411) conjugated gold NPs (AS1411-Au NPs). The AS1411-Au NPs/Au@PC NP is used as a targeting agent in laser desorption/ionization mass spectrometry (LDI-MS)-based tumor tissue imaging. Self-assembled core-shell Au@PC NPs are synthesized by a simple reaction of tetrachloroaurate(III) with catechin. Au@PC NPs with a well-defined and dense poly(catechin) shell (~40-60 nm) on the surface of each Au core (~60-80 nm) are obtained through careful control of the ratio of catechin to gold ions, as well as the pH of the reaction solution. Furthermore, we have shown that AS1411-conjugated Au NPs (13-nm) self-assembled on Au@PC NP can from a satellite-like gold nanocomposite. The high density of AS1411-Au NPs on the surface of Au@PC NP enhances multivalent binding with nucleolin molecules on tumor cell membranes. We have employed LDI-MS to detect AS1411-Au NPs/Au@PC NPs labeled nucleolin-overexpressing MCF-7 breast cancer cells through the monitoring of Au cluster ions ([Au_n]⁺; 1 ≤ n ≤ 3). The ultrahigh signal amplification from Au NPs through the formation of a huge number of [Au_n]⁺ ions results in a sensing platform with a limit of detection of 100 MCF-7 cells mL^-1. Further, we have applied the satellite-like AS1411-Au NPs/Au@PC NP nanocomposite as a labeling agent for tumor tissue imaging by LDI-MS. Our nanocomposite-assisted LDI-MS imaging platform can be extended for simultaneous analysis of different tumor markers on cell membranes when using different ligand-modified metal nanoparticles.

Synthesis and Properties of Hemostatic and Bacteria-Responsive in Situ Hydrogels for Emergency Treatment in Critical Situations

Immediate hemorrhage control and infection prevention are pivotal for saving lives in critical situations such as battlefields, natural disasters, traffic accidents, and so on. In situ hydrogels are promising candidates, but their mechanical strength is often not strong enough for use in critical situations. In this study, we constructed three hydrogels with different amounts of Schiff-base moieties from 4-arm-PEG-NH2, 4-arm-PEG-NHS, and 4-arm-PEG-CHO in which vancomycin was incorporated as an antimicrobial agent. The hydrogels possess porous structures, excellent mechanical strength, and high swelling ratio. The cytotoxicity studies indicated that the composite hydrogel systems possess good biocompatibility. The Schiff bases incorporated improve the adhesiveness and endow the hydrogels with bacteria-sensitivity. The in vivo hemostatic and antimicrobial experiments on rabbits and pigs demonstrated that the hydrogels are able to aid in rapid hemorrhage control and infection prevention. In summary, vancomycin-loaded hydrogels may be excellent candidates as hemostatic and antibacterial materials for first aid treatment of the wounded in critical situations.

Monitoring Cluster Ions Derived from Aptamer-Modified Gold Nanofilms under Laser Desorption/Ionization for the Detection of Circulating Tumor Cells

In this paper, we describe the use of pulsed laser desorption/ionization mass spectrometry (LDI-MS) for the detection of tumor cells through the analysis of gold cluster ions [Aun](+) from aptamer-modified gold nanofilms (Au NFs). We observed not only the transformation of the Au NFs into gold nanoparticles (Au NPs) but also the formation of gaseous gold cluster ions ([Au(n)](+); n = 1-5) under irradiation with a nanosecond pulsed laser. The size and density of the formed Au NPs and the abundance of [Au(n)](+) ions were both highly dependent on the thickness of the Au NFs (10-100 nm). Thin Au NFs tended to form highly dense Au NPs on the substrate and favored the desorption and ionization of gold cluster ions. The signal intensities of the [Au(n)](+) species, monitoring using mass spectrometry, decreased upon increasing the thickness of the Au NF from 10 to 100 nm and after modification with thiolated DNA. Furthermore, we found that Au NFs modified with mucin1-binding aptamer (AptMUC1-Au NFs) could selectively enrich MCF-7 cells (human breast adenocarcinoma cell line) in blood samples; coupled with LDI-MS analysis of the [Au(n)](+) ions, we could detect MCF-7 cells selectively in blood samples at abundances as low as 10 cells. This approach offers the advantages of high sensitivity, selectivity, and throughput for the detection of circulating tumor cells, and has great potential for use as a powerful analytical platform for clinical diagnoses of tumor metastasis.