Using Biofunctionalized Nanoparticles To Probe Pathogenic Bacteria

Europium Ion-Based Magnetic-Trapping and Fluorescence-Sensing Method for Detection of Pathogenic Bacteria

Europium ions (Eu3+) have been utilized as a fluorescence-sensing probe for a variety of analytes, including tetracycline (TC). When Eu3+ is chelated with TC, its fluorescence can be greatly enhanced. Moreover, Eu3+ possesses 6 unpaired electrons in its f orbital, which makes it paramagnetic. Being a hard acid, Eu3+ can chelate with hard bases, such as oxygen-containing functional groups (e.g., phosphates and carboxylates), present on the cell surface of pathogenic bacteria. Due to these properties, in this study, Eu3+ was explored as a magnetic-trapping and sensing probe against pathogenic bacteria present in complex samples. Eu3+ was used as a magnetic probe to trap bacteria such as Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Acinetobacter baumannii, Bacillus cereus, and Pseudomonas aeruginosa. The addition of TC facilitated the easy detection of magnetic Eu3+-bacterium conjugates through fluorescence spectroscopy, with a detection limit of approximately ∼104 CFU mL-1. Additionally, matrix-assisted laser desorption/ionization mass spectrometry was employed to differentiate bacteria tapped by our magnetic probes.

Capture and elimination of Staphylococcus aureus based on Langmuir–Blodgett MnO2 nanowire monolayer promotes infected wound healing

An antibacterial membrane, consisting of PDMS and TBBPA coated with a human immunoglobulin G modified MnO₂ nanowire monolayer, was applied to capture and eliminate Staphylococcus aureus and promote infected wound healing.

Superparamagnetic nickel colloidal nanocrystal clusters with antibacterial activity and bacteria binding ability

Recent progress in synthetic nanotechnology and the ancient use of metals in food preservation and the antibacterial treatment of wounds have prompted the development of nanometallic materials for antimicrobial applications^1-4. However, the materials designed so far do not simultaneously display antimicrobial activity and the capability of binding and capturing bacteria and spores. Here, we develop a one-step pyrolysis procedure to synthesize monodisperse superparamagnetic nickel colloidal nanocrystal clusters (SNCNCs), which show both antibacterial activity and the ability to bind Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria, as well as bacterial spores. The SNCNCs are formed from a rapid burst of nickel nanoparticles, which self-assemble slowly into clusters. The clusters can magnetically extract 99.99% of bacteria and spores and provide a promising approach for the removal of microbes, including hard-to-treat microorganisms. We believe that our work illustrates the exciting opportunities that nanotechnology offers for alternative antimicrobial strategies and other applications in microbiology.

Inhibition of the lethality of Shiga-like toxin-1 by functional gold nanoparticles

Escherichia coli O157:H7 is a pathogen, which can generate Shiga-like toxins (SLTs) and cause hemolytic-uremic syndrome. Foodborne illness outbreaks caused by E. coli O157:H7 have become a global issue. Since SLTs are quite toxic, effective medicines that can reduce the damage caused by SLTs should be explored. SLTs consist of a single A and five B subunits, which can inhibit ribosome activity for protein synthesis and bind with the cell membrane of host cells, respectively. Pigeon ovalbumin (POA), i.e. a glycoprotein, is abundant in pigeon egg white (PEW) proteins. The structure of POA contains Gal-α(1→4)-Gal-β(1→4)-GlcNAc ligands, which have binding affinity toward the B subunit in SLT type-1 (SLT-1B). POA immobilized gold nanoparticles (POA-Au NPs) can be generated by reacting PEW proteins with aqueous tetrachloroauric acid in one-pot. The generated POA-Au NPs have been demonstrated to have selective trapping-capacity toward SLT-1B previously. Herein, we explore that POA-Au NPs can be used as protective agents to neutralize the toxicity of SLT-1 in SLT-1-infected model cells. The results show that the cells can be completely rescued when a sufficient amount of POA-Au NPs is used to treat the SLT-1-infected cells within 1 h.

Magnetic immobilization of bacteria using iron oxide nanoparticles

Bacterial cell immobilization is a novel technique used in many areas of biosciences and biotechnology. Iron oxide nanoparticles have attracted much attention in bacterial cell immobilization due to their unique properties such as superparamagnetism, large surface area to volume ratio, biocompatibility and easy separation methodology. Adhesion is the basis behind many immobilization techniques and various types of interactions determine bacterial adhesion. Efficiency of bacterial cell immobilization using iron oxide nanoparticles (IONs) generally depends on the physicochemical properties of the IONs and surface properties of bacterial cells as well as environmental/culture conditions. Bacteria exhibit various metabolic responses upon interaction with IONs, and the potential applications of iron oxide nanoparticles in bacterial cell immobilization will be discussed in this work.

Selective Detection of Shiga-like Toxin 1 from Complex Samples Using Pigeon Ovalbumin Functionalized Gold Nanoparticles as Affinity Probes

Escherichia coli O157:H7 is a foodborne pathogen. This bacterial strain can generate Shiga-like toxins (SLTs), which can cause serious sickness and even death. Thus, it is important to develop effective and sensitive methods that can be used to rapidly identify the presence of SLTs from complex samples. Pigeon egg white (PEW) contains abundant glycoproteins, including pigeon ovalbumin (POA) (∼60%). POA possesses Gal-α(1→4)-Gal-β(1→4)-GlcNAc termini, which can recognize the B subunits in SLT type 1 (SLT-1B). Thus, POA is a suitable probe for trapping SLT-1B. In this work, we used PEW proteins as starting materials to react with aqueous tetrachloroauric acid for generation of PEW-protein-immobilized gold nanoparticles (AuNPs@PEW) via one-pot reactions. We demonstrated that the generated AuNPs@PEW were mainly dominated by POA-immobilized Au NPs. The as-prepared AuNPs@PEW were used as affinity probes to selectively probe SLT-1B from complex cell lysates derived from E. coli O157:H7. The selective trapping step can be completed within ∼90 s under microwave heating (power = 450 W) to enrich sufficient SLT-1B for matrix-assisted laser desorption/ionization (MALDI) mass spectrometric analysis. Furthermore, this approach can be used to detect SLT-1B at a concentration as low as ∼40 pM. The feasibility of using the proposed method to selectively detect SLT-1B from ham contaminated by E. coli O157:H7 was also demonstrated.

Large protein analysis of Staphylococcus aureus and Escherichia coli by MALDI TOF mass spectrometry using amoxicillin functionalized magnetic nanoparticles

Bacteria or their protein and peptide entity enrichment using biomolecules-functionalized magnetic nanoparticles, and analysis by matrix assisted laser desorption/ionization mass spectrometry (MALDI MS) is a promising technique to analyze microorganisms. High and low molecular weight proteins like penicillin-binding proteins are responsible for final step synthesis of peptidoglycan biosynthesis; those are the target of lactam antibiotics. In this paper, we synthesized magnetic nanoparticles (mag-NPs) and further modified them with 3-aminopropyltriethoxysilane, and then the β-lactam antibiotic amoxicillin was covalently linked to their surface. β-Lactam group attributes as penicillin binding proteins (PBPs) in bacteria. Staphylococcus aureus and Escherichia coli were used as model bacteria for enrichment based on the β-lactam affinity of magnetic nanoparticles, and then the bacteria were easily separated by an external magnet. Several high molecular weight penicillin binding proteins (PBPs) were detected by MALDI MS containing 10(4) and 10(3) colony-forming unit (cfu) per milileter (mL) of S. aureus and E. coli, respectively. In the case of E. coli, higher molecular weight PBPs were observed at 20 to 55 kDa in MALDI mass spectra. However, S. aureus bacteria resulted with femAB operon-based proteins, with molecular weight of 49570.4 Da, by MALDI MS after using amoxicillin functionalized-mag-NPs. The current approach provides an effective bacteria detection and preconcentration method that has high potential in the near future for fast and sensitive diagnosis of pathogenic bacteria infection. Graphical Abstract Schematic for large proteins analysis by MALDI TOF MS (a) mag-NPs and bacterial interaction (b) Penicillin binding proteins trapping by Amox-mag-NPs.

Advanced Nanobiomaterials: Vaccines, Diagnosis and Treatment of Infectious Diseases

The use of nanoparticles has contributed to many advances due to their important properties such as, size, shape or biocompatibility. The use of nanotechnology in medicine has great potential, especially in medical microbiology. Promising data show the possibility of shaping immune responses and fighting severe infections using synthetic materials. Different studies have suggested that the addition of synthetic nanoparticles in vaccines and immunotherapy will have a great impact on public health. On the other hand, antibiotic resistance is one of the major concerns worldwide; a recent report of the World Health Organization (WHO) states that antibiotic resistance could cause 300 million deaths by 2050. Nanomedicine offers an innovative tool for combating the high rates of resistance that we are fighting nowadays, by the development of both alternative therapeutic and prophylaxis approaches and also novel diagnosis methods. Early detection of infectious diseases is the key to a successful treatment and the new developed applications based on nanotechnology offer an increased sensibility and efficiency of the diagnosis. The aim of this review is to reveal and discuss the main advances made on the science of nanomaterials for the prevention, diagnosis and treatment of infectious diseases. Highlighting innovative approaches utilized to: (i) increasing the efficiency of vaccines; (ii) obtaining shuttle systems that require lower antibiotic concentrations; (iii) developing coating devices that inhibit microbial colonization and biofilm formation.

Affinity capture using peptide-functionalized magnetic nanoparticles to target Staphylococcus aureus

Staphylococcus aureus, a commonly found pathogen, can cause food poisoning and infections. Thus, it is necessary to develop analytical methods for the rapid screening of S. aureus in suspicious samples. Magnetic nanoparticles (MNPs) are widely used as affinity probes to selectively enrich target species from complex samples because of their high specific surface area and magnetic properties. The MNP surface should be functionalized to have the capability to target specific species. We herein propose a straightforward method to functionalize aluminum oxide-coated iron oxide (Fe3O4@Al2O3) MNPs with the peptide HHHHHHDEEGLFVD (D). The peptide D was comprised of three domains: polyhistidine (H6) used as the linker, DEE added as the spacer, and GLFVD used for targeting S. aureus. D was immobilized on the surface of Fe3O4@Al2O3 MNPs through H6-Al chelation. Our results showed that the D-functionalized Fe3O4@Al2O3 MNPs (D-Fe3O4 MNPs) possess the capability to target S. aureus. The selective trapping experiments were conducted under microwave-heating for only 60 s, and sufficient bacterial cells were trapped by the MNPs to be identified by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). We demonstrated that the D-Fe3O4@Al2O3 MNPs combined with MALDI-MS can be used to rapidly characterize trace amounts of S. aureus in complex juice and egg samples.

State-of-the-art nanoplatform-integrated MALDI-MS impacting resolutions in urinary proteomics

Urine proteomics has become a subject of interest, since it has led to a number of breakthroughs in disease diagnostics. Urine contains information not only from the kidney and the urinary tract but also from other organs, thus urinary proteome analysis allows for identification of biomarkers for both urogenital and systemic diseases. The following review gives a brief overview of the analytical techniques that have been in practice for urinary proteomics. MALDI-MS technique and its current application status in this area of clinical research have been discussed. The review comments on the challenges facing the conventional MALDI-MS technique and the upgradation of this technique with the introduction of nanotechnology. This review projects nano-based techniques such as nano-MALDI-MS, surface-assisted laser desorption/ionization, and nanostructure-initiator MS as the platforms that have the potential in trafficking MALDI-MS from the lab to the bedside.

Detection of Staphylococcus aureus by functional gold nanoparticle-based affinity surface-assisted laser desorption/ionization mass spectrometry

Staphylococcus aureus is one of the common pathogenic bacteria responsible for bacterial infectious diseases and food poisoning. This study presents an analytical method based on the affinity nanoprobe-based mass spectrometry that enables detection of S. aureus in aqueous samples. A peptide aptamer DVFLGDVFLGDEC (DD) that can recognize S. aureus and methicillin-resistant S. aureus (MRSA) was used as the reducing agent and protective group to generate DD-immobilized gold nanoparticles (AuNPs@DD) from one-pot reactions. The thiol group from cysteine in the peptide aptamer, i.e., DD, can interact with gold ions to generate DD-immobilized AuNPs in an alkaline solution. The generated AuNPs@DD has an absorption maximum at ∼518 nm. The average particle size is 7.6 ± 1.2 nm. Furthermore, the generated AuNPs@DD can selectively bind with S. aureus and MRSA. The conjugates of the target bacteria with AuNPs were directly analyzed by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The gold ions generated from the AuNPs@DD anchored on the target bacteria were monitored. Gold ions (m/z 197 and 394) were only generated from the conjugates of the target bacterium-AuNP@DD in the SALDI process. Thus, the gold ions could be used as the indicators for the presence of the target bacteria. The detection limit of S. aureus using this method is in the order of a few tens of cells. The low detection limit is due to the ease of generation of gold cluster ion derived from AuNPs under irradiation with a 355 nm laser beam. Apple juice mixed with S. aureus was used as the sample to demonstrate the suitability of the method for real-world application. Because of its low detection limit, this approach can potentially be used to screen the presence of S. aureus in complex samples.

Silver nanostructures in laser desorption/ionization mass spectrometry and mass spectrometry imaging

Silver nanoparticles have been successfully applied as a matrix replacement for the laser desorption/ionization time-of-flight mass spectrometry (LDI-ToF-MS).

On-chip integration of novel Au electrode with a higher order three-dimensional layer stack nanostructure for surface-enhanced Raman spectroscopy

We develop a novel in situ surface-enhanced Raman spectroscopy (SERS) platform with three-dimensional nanostructure gold electrodes using the competitive self-assembly between dielectrophoresis and convective aggregation.

Recent advances in bacteria identification by matrix-assisted laser desorption/ionization mass spectrometry using nanomaterials as affinity probes

Identifying trace amounts of bacteria rapidly, accurately, selectively, and with high sensitivity is important to ensuring the safety of food and diagnosing infectious bacterial diseases. Microbial diseases constitute the major cause of death in many developing and developed countries of the world. The early detection of pathogenic bacteria is crucial in preventing, treating, and containing the spread of infections, and there is an urgent requirement for sensitive, specific, and accurate diagnostic tests. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an extremely selective and sensitive analytical tool that can be used to characterize different species of pathogenic bacteria. Various functionalized or unmodified nanomaterials can be used as affinity probes to capture and concentrate microorganisms. Recent developments in bacterial detection using nanomaterials-assisted MALDI-MS approaches are highlighted in this article. A comprehensive table listing MALDI-MS approaches for identifying pathogenic bacteria, categorized by the nanomaterials used, is provided.

Rapid and direct MALDI-MS identification of pathogenic bacteria from blood using ionic liquid-modified magnetic nanoparticles (Fe3O4@SiO2)

A novel method for pathogenic bacteria identification directly from blood samples using cationic ionic liquid-modified magnetic nanoparticles (CILMS) is reported.

Lysozyme-encapsulated gold nanocluster-based affinity mass spectrometry for pathogenic bacteria

RATIONALE

Bacterial infections can be difficult to treat and can lead to irreversible damage to patients if proper treatment is not provided in time. Additionally, the emerging threat from antibiotic-resistant bacterial strains makes medical treatment even more difficult. Thus, rapid identification of infected bacterial strains is essential to assist diagnostics and medical treatment.

METHODS

Lysozymes are glycoside hydrolases that can bind with peptidoglycans on bacterial cell walls. In this work, we demonstrated that lysozyme-encapsulated gold nanoclusters (lysozyme-AuNCs) with red photoluminescence can be used as affinity probes to concentrate pathogenic bacteria. After bacteria had been probed by the lysozyme-AuNCs in a sample solution, the lysozyme-AuNC-bacteria conjugates were readily spun down at a low centrifugation speed. The red emission from the AuNCs on the conjugates could be visualized with the naked eye under illumination of ultraviolet light. The bacteria in the conjugates can be identified by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with principal component analysis (PCA).

RESULTS

We demonstrated that pathogenic bacteria including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, pandrug-resistant Acinetobacter baumannii, Staphylococcus aureus, Enterococcus faecalis, and vancomycin-resistant Enterococcus faecalis (VRE) can be readily concentrated by the lysozyme-AuNCs and distinguished by the results combining MALDI-MS and PCA. Additionally, the possibility of using the current approach to differentiate E. faecalis from VRE was also demonstrated. The lowest detection concentration for E. coli using the current approach is ~10(6) cells/mL.

CONCLUSIONS

The results indicated that the lysozyme-AuNCs are effective affinity probes for Gram-positive and Gram-negative bacteria. By combining the results from MALDI-MS and PCA, different bacteria can be easily distinguished. The current approach can be potentially used to assist the identification of bacteria from biological fluids.

A comparative study on the mode of interaction of different nanoparticles during MALDI-MS of bacterial cells

We propose the benefits of preincubation during nanoparticle-assisted bacterial analysis, where the bacteria are grown along with the nanoparticles. We were able to obtain a two to ten fold enhancement of bacterial signals in 3 h compared to the generally used methodology followed in previous literature. The previous literature method required a long time (18 h) to obtain such an enhancement. We probe the interactions of two bacteria, Staphylococcus aureus and Pseudomonas aeruginosa, with Ag, NiO, Pt TiO(2) and ZnO nanoparticles via transmission electron microscopy, ultraviolet spectroscopy and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Based on these results, we propose a mechanism for interaction of these five nanoparticles with bacteria. Two mechanisms were observed for the interactions: (1) Mechanism A is proposed for the Pt and NiO NPs which functioned based on affinity for bacterial cells. (2) Mechanism B was proposed for the bactericidal NPs such as TiO(2), ZnO and Ag NPs. The results indicate that the success of the unmodified NPs in MALDI-MS bacterial studies lies in following the ideal protocol for incubation at the ideal concentrations.

Human serum albumin stabilized gold nanoclusters as selective luminescent probes for Staphylococcus aureus and methicillin-resistant Staphylococcus aureus

In this work, human serum albumin (HSA) stabilized gold nanoclusters (HSA-AuNCs) with reddish photoluminescence were used as sensing probes for pathogenic bacteria including Enterobacter cloacae, Escherichia coli J96, Pseudomonas aeruginosa, pandrug-resistant Acinetobacter baumannii (PDRAB), Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Streptococcus pyogenes, and vancomycin-resistant Enterococcus faecalis (VRE). We discovered that HSA-AuNCs have unique affinity with S. aureus and MRSA. In addition to demonstrating the selective sensing ability of HSA-AuNCs toward S. aureus and MRSA, the binding peptide motifs identified from HSA-AuNCs were characterized by mass spectrometry. The identified binding peptides were further used as the reducing and stabilizing agents for generation of peptide-bound AuNCs (Pep-AuNCs). The generated Pep-AuNCs were demonstrated to have the binding affinities with S. aureus and MRSA.

Future perspective of nanoparticle interaction-assisted laser desorption/ionization mass spectrometry for rapid, simple, direct and sensitive detection of microorganisms

The introduction of nanoparticles into mass spectrometric research greatly influenced the applicability of this technique into various omics. Surface-modified or functionalized nanoparticles (NPs) have recently extended the use of mass spectrometry into microorganism research. We survey the application of unmodified NPs, for microorganism research, on the basis of our expertise in this area within the recent years in this decade. The use of unmodified NPs in mass spectrometry, especially with respect to microorganisms, is an untreaded research area, which we have ventured to probe and have been fruitful. On the basis of our experience, we provide an insight into the principle behind the use of unmodified NPs and provide guidelines to be followed to obtain significant results. We also brief the current scenario of nanoparticle interaction-assisted laser desorption/ionization mass spectrometry (NPILDI-MS) for rapid, simple, direct and sensitive detection of microorganisms on the basis of our past and present reports, quoting examples of successful application of this technique. Finally, we address the future of the NPILDI-MS technique and the tools needed to reach those visions.

Gold nanoparticles in biomedical applications: recent advances and perspectives

Gold nanoparticles (GNPs) with controlled geometrical, optical, and surface chemical properties are the subject of intensive studies and applications in biology and medicine. To date, the ever increasing diversity of published examples has included genomics and biosensorics, immunoassays and clinical chemistry, photothermolysis of cancer cells and tumors, targeted delivery of drugs and antigens, and optical bioimaging of cells and tissues with state-of-the-art nanophotonic detection systems. This critical review is focused on the application of GNP conjugates to biomedical diagnostics and analytics, photothermal and photodynamic therapies, and delivery of target molecules. Distinct from other published reviews, we present a summary of the immunological properties of GNPs. For each of the above topics, the basic principles, recent advances, and current challenges are discussed (508 references).

Nanoparticle-based microextraction techniques in bioanalysis

Nanoparticles (NPs) have attracted a great deal of attention in the last decade due to their exceptional mechanical, optical and electronic properties. This article deals with the use of NPs as probes for the extraction of biomolecules from biological samples. In this context, NPs present some advantages compared with conventional sorbents. Their high surface-to-volume ratio, easy synthetic (especially for inorganic NPs) and derivatization procedures, and their biocompatibility make them a powerful alternative. In order to provide a systematic approach to the topic, NPs have been divided into two general groups attending to their chemical nature. Carbon-based (e.g., fullerene and nanotubes) and inorganic NPs (e.g., gold and magnetic NPs) are considered in depth, explaining their main properties and applications. After these critical considerations, the most important conclusions and essential trends in this field are also outlined.

Advances in mass spectrometry for the identification of pathogens

Mass spectrometry (MS) has become an important technique to identify microbial biomarkers. The rapid and accurate MS identification of microorganisms without any extensive pretreatment of samples is now possible. This review summarizes MS methods that are currently utilized in microbial analyses. Affinity methods are effective to clean, enrich, and investigate microorganisms from complex matrices. Functionalized magnetic nanoparticles might concentrate traces of target microorganisms from sample solutions. Therefore, nanoparticle-based techniques have a favorable detection limit. MS coupled with various chromatographic techniques, such as liquid chromatography and capillary electrophoresis, reduces the complexity of microbial biomarkers and yields reliable results. The direct analysis of whole pathogenic microbial cells with matrix-assisted laser desorption/ionization MS without sample separation reveals specific biomarkers for taxonomy, and has the advantages of simplicity, rapidity, and high-throughput measurements. The MS detection of polymerase chain reaction (PCR)-amplified microbial nucleic acids provides an alternative to biomarker analysis. This review will conclude with some current applications of MS in the identification of pathogens.

A renewable and ultrasensitive electrochemiluminescence immunosenor based on magnetic RuL@SiO2-Au~RuL-Ab2 sandwich-type nano-immunocomplexes

An ultrasensitive and renewable electrochemiluminescence (ECL) immunosensor was developed for the detection of tumor markers by combining a newly designed trace tag and streptavidin-coated magnetic particles (SCMPs). The trace tag (RuL@SiO(2)-Au~RuL-Ab2) was prepared by loading Ru(bpy)(3)(2+)(RuL)-conjuged secondary antibodies (RuL-Ab2) on RuL@SiO(2) (RuL-doped SiO(2)) doped Au (RuL@SiO(2)-Au). To fabricate the immunosensor, SCMPs were mixed with biotinylated AFP primary antibody (Biotin-Ab1), AFP, and RuL@SiO2-Au~RuL-Ab2 complexes, then the resulting SCMP/Biotin-Ab1/AFP/RuL@SiO2-Au~RuL-Ab2 (SBAR) sandwich-type immunocomplexes were absorbed on screen printed carbon electrode (SPCE) for detection. The immunocomplexes can be easily washed away from the surface of the SPCE when the magnetic field was removed, which made the immunosensor reusable. The present immunosensor showed a wide linear range of 0.05-100 ng mL(-1) for detecting AFP, with a low detection limit of 0.02 ng mL(-1) (defined as S/N = 3). The method takes advantage of three properties of the immunosensor: firstly, the RuL@SiO(2)-Au~RuL-Ab2 composite exhibited dual amplification since SiO(2) could load large amount of reporter molecules (RuL) for signal amplification. Gold particles could provide a large active surface to load more reporter molecules (RuL-Ab2). Accordingly, through the ECL response of RuL and tripropylamine (TPA), a strong ECL signal was obtained and an amplification analysis of protein interaction was achieved. Secondly, the sensor is renewable because the sandwich-type immunocomplexes can be readily absorbed or removed on the SPCE's surface in a magnetic field. Thirdly, the SCMP modified probes can perform the rapid separation and purification of signal antibodies in a magnetic field. Thus, the present immunosensor can simultaneously realize separation, enrichment and determination. It showed potential application for the detection of AFP in human sera.

Sample preparation methods for MALDI-MS profiling of bacteria

Direct matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) bacterial cell or lysate analysis appears to meet all the criteria required for a rapid and reliable analytical microorganism identification and taxonomical classification tool. Few-minute analytical procedure providing information extending up to sub-species level underlines the potential of the MALDI-MS profiling in comparison with other methods employed in the field. However, the quality of MALDI-MS profiles and consequently the performance of the method are influenced by numerous factors, which involve particular steps of the sample preparation procedure. This review is aimed at advances in development and optimization of the MALDI-MS profiling methodology. Approaches improving the quality of the MALDI-MS profiles and universal feasibility of the method are discussed.

A three-dimensional, magnetic and electroactive nanoprobe for amperometric determination of tumor biomarkers

A novel electrochemical immunosensor for tumor biomarker detection based on three-dimensional, magnetic and electroactive nanoprobes was developed in this study. To fabricate the nanoprobes, negatively charged Fe(3)O(4) nanoparticles (Fe(3)O(4) NPs) and gold nanoparticles (Au NPs) were first loaded on the surface of multiple wall carbon nanotubes (MCNTs) which were functioned with redox-active hemin and cationic polyelectrolyte poly(dimethyldiallylammonium chloride) (PDDA). Using alpha fetoprotein (AFP) as a model analyte, AFP antibody (anti-AFP) was absorbed on the surface of Au NPs, bovine serum albumin (BSA) was then used to block sites against non-specific binding, and finally formed anti-AFP/Au NPs/Fe(3)O(4)/hemin/MCNTs named anti-AFP nanoprobes. When the target antigen AFP was present, it interacted with anti-AFP and formed an antigen-antibody complex on the nanoprobe interface. This resulted in a decreased electrochemical signal of hemin for quantitative determination of AFP when immobilized onto the screen-printed working electrode (SPCE). The results showed that the nanoprobe-based electrochemical immunosensor was sensitive to AFP detection at a concentration of 0.1 to 200 ng·mL(-1) with a detection limit of 0.04 ng·mL(-1), it also demonstrated good selectivity against other interferential substances. The electroactive nanoprobes can be massively prepared, easily immobilized on the SPCE for target detection and rapidly renewed with a magnet. The proposed immunosensor is fast, simple, sensitive, stable, magnet-controlled, nontoxic, label-free and reproducible.

Multifunctional nanoparticles as simulants for a gravimetric immunoassay

Immunoassays are important tools for the rapid detection and identification of pathogens, both clinically and in the research laboratory. An immunoassay with the potential for the detection of influenza was developed and tested using hemagglutinin (HA), a commonly studied glycoprotein found on the surface of influenza virions. Gold nanoparticles were synthesized, which present multiple peptide epitopes, including the HA epitope, in order to increase the gravimetric response achieved with the use of a QCM immunosensor for influenza. Specifically, epitopes associated with HA and FLAG peptides were affixed to gold nanoparticles by a six-mer PEG spacer between the epitope and the terminal cysteine. The PEG spacer was shown to enhance the probability for interaction with antibodies by increasing the distance the epitope extends from the gold surface. These nanoparticles were characterized using thermogravimetric analysis, transmission electron microscopy, matrix-assisted laser desorption/ionization-time of flight, and (1)H nuclear magnetic resonance analysis. Anti-FLAG and anti-HA antibodies were adhered to the surface of a QCM, and the response of each antibody upon exposure to HA, FLAG, and dual functionalized nanoparticles was compared with binding of Au-tiopronin nanoparticles and H5 HA proteins from influenza virus (H5N1). Results demonstrate that the immunoassay was capable of differentiating between nanoparticles presenting orthogonal epitopes in real-time with minimal nonspecific binding. The detection of H5 HA protein demonstrates the logical extension of using these nanoparticle mimics as a safe positive control in the detection of influenza, making this a vital step in improving influenza detection methodology.

Fe3O4/TiO2 core/shell magnetic nanoparticle-based photokilling of pathogenic bacteria

Aims: We demonstrate a photokilling approach for pathogenic bacteria using magnetic nanoparticles as photokilling nanoprobes. Materials & methods: The nanoprobes are composed of iron oxide/titania (Fe3O4/TiO2) core/shell magnetic nanoparticles. The titanium layer on the magnetic nanoprobes plays two roles: as a photokilling agent and as an affinity substrate for pathogenic bacteria. The magnetic property of the nanoprobes allows the resultant nanoprobe–target species conjugates to be readily aggregated at a small spot under external magnetic field for conducting photokilling treatment. Therefore, damage to nontarget cells can be reduced. Results: The results show that Fe3O4/TiO2 core/shell magnetic nanoparticles do not only have the capacity to target pathogenic bacteria, including Gram-negative, Gram-positive and antibiotic-resistant bacteria, but they can also be used to effectively inhibit the cell growth of the bacteria (>99.9%) targeted by the magnetic nanoparticles under irradiation of a low-power UV lamp (λmax ∼306 nm, 0.412 mW/cm2) within 15 min. Conclusion: The potential application of this approach is in the treatment of cutaneous bacterial infections.

SERS-based sandwich immunoassay using antibody coated magnetic nanoparticles for Escherichia coli enumeration

A method combining immunomagnetic separation (IMS) and surface-enhanced Raman scattering (SERS) was developed to enumerate Escherichia coli (E. coli). Gold-coated magnetic spherical nanoparticles were prepared by immobilizing biotin-labeled anti-E. coli antibodies onto avidin-coated magnetic nanoparticles and used in the separation and concentration of the E. coli cells. Raman labels have been constructed using rod shaped gold nanoparticles coated with 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB) and subsequently with a molecular recognizer. Then DTNB-labeled gold nanorods were interacted with gold-coated magnetic spherical nanoparticle-antibody-E. coli complex. The capture efficiency and calibration graphs were obtained and examined in different E. coli concentrations (10(1)-10(7) cfu mL(-1)). The correlation between the concentration of bacteria and SERS signal was found to be linear within the range of 10(1)-10(4) cfu mL(-1) (R(2) = 0.992). The limit of detection (LOD) and limit of quantification (LOQ) values of the developed method were found to be 8 and 24 cfu mL(-1), respectively. The selectivity of the developed immunoassay was examined with Enterobacter aerogenes, Enterobacter dissolvens, and Salmonella enteriditis which did not produce any significant response. The ability of the immunoassay to detect E. coli in real water samples was also investigated and the results were compared with the experimental results from plate-counting methods. There was no significant difference between the methods that were compared (p > 0.05). This method is rapid and sensitive to target organisms with a total analysis time of less than 70 min.

Amine-functionalized magnetic nanoparticles for rapid capture and removal of bacterial pathogens

Interest in magnetic nanoparticles for capturing bacteria arises from a variety of attributes, including the similar size of nanoparticles, magnetic behavior, and attached biomolecules such as proteins and nucleotide probes. Here we report the application of amine-functionalized magnetic nanoparticles (AF-MNPs) for rapid and efficient capture and removal of bacterial pathogens. The AF-MNPs are used without the need for any further modifications with affinity biomolecules. The positive charges on the surface of AF-MNPs can promote strong electrostatic interaction with negatively charged sites on the surface of bacterial pathogens to exhibit efficient adsorptive ability. The hydrophobic interaction between the pendant propyl group of the amine functionality and the bacteria also plays a supplementary role. The amine groups on the surface of the magnetic nanoparticle are robust and inexpensive ligands to ensure a high binding affinity to at least eight different species of Gram-positive and Gram-negative bacteria. The amount of AF-MNPs, pH of phosphate buffer solution, and ionic strength are crucial in mediating fast and effective interactions between AF-MNPs and bacteria. The AF-MNPs allow rapid removal of bacteria from water samples, food matrixes, and a urine sample with efficiency from 88.5% to 99.1%. Though amino group offers less specificity/selectivity than biomolecules such as antibodies, AF-MNPs are attractive for capturing a wide range of bacteria.