Simple detection of gluten in commercial gluten-containing samples with a novel nanoflower electrosensor made of molybdenum disulfide with comparison of the ELISA method.

In this study, a new electrochemical sensor based on molybdenum disulfide (MoS2) nanoflowers/glassy carbon electrode (GCE was created for the sensitive detection of gluten. The prepared nanocatalysts were characterized using scanning electron microscopy with energy dispersive spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. The effects of the prepared nanocatalysts, pH value, and dropping amounts on the results were examined in detail. The electrochemical performance of the developed sensor (MoS2 nanoflowers/GCE) was then evaluated using differential pulse voltammetry, and the sensor was found to have significant electrochemical activity against gluten. A substantial linear connection was observed in the range of 0.5-100 ppm of gluten concentration under optimum experimental circumstances, and the detection limit between peak current and gluten concentration was determined as 1.16 ppm. The findings showed that the MoS2 nanoflowers/GCE gluten sensor has exceptional selectivity and stability. Finally, the generated electrochemical sensor was effectively utilized for gluten detection in commercial gluten-containing materials with a detection limit of 0.1652 ppm. Thus, the developed MoS2 nanoflowers/GCE sensor offers a potential method for the detection of other molecules and is a promising candidate for gluten detection in commercial samples.

Emulsifying properties of plant-derived polypeptide and their conjugates: a self-consistent-field calculation study of the impact of hydrolysis.

By considering the hydrolysates of soy protein produced by trypsin as an example, the emulsion stabilizing properties of plant-based protein fragments have been investigated theoretically. We apply Self-Consistent-Field (SCF) calculations to determine the colloidal interactions induced between a pair of droplets stabilized by adsorbed layers of various soy protein fragments. The study is extended to conjugates of such polypeptides, formed by covalent bonding with a suitable hydrophilic sidechain (e.g. a polysaccharide). Our results show that the relatively longer fragments, with a greater number of hydrophobic amino acids, will display a stronger degree of adsorption affinity compared to the smaller hydrolysates, even where the latter may have a higher overall ratio of hydrophobic residues. This suggested that the degree of protein hydrolysis should be carefully controlled and limited to modest values to avoid the generation of a large number of short polypeptides, while still sufficient to improve solubility. While the emulsion stabilizing performance of a protein fragment type is strongly dependent on the conformation it adopts on the interface, we find this to be less critical for the conjugated polypeptides. However, we argue that with increasing degree of hydrolysis, many small fragments will not have the chance to form bonds with polysaccharides. It is demonstrated that the abundance of these unreacted polypeptides in the system severely reduces the efficiency of the conjugated longer protein fragments, preventing their presence on the surface of the droplets through competitive adsorption process.

Fabrication of glucose bioelectrochemical sensor based on Au@Pd core-shell supported by carboxylated graphene oxide.

The study presents a novel electrochemical glucose biosensor based on glucose oxidase (GOx) immobilized on Au@Pd core-shell nanoparticles supported on carboxylated graphene oxide (cGO). The immobilization of GOx was achieved by cross-linking the chitosan biopolymer (CS) including Au@Pd/cGO and glutaraldehyde (GA) on a glassy carbon electrode. The analytical performance of GCE/Au@Pd/cGO-CS/GA/GOx was investigated using amperometry. The biosensor had fast response time (5.2 ± 0.9 s), a satisfactory linear determination range between 2.0 × 10-5 and 4.2 × 10-3 M, and limit of detection of 10.4 µM. The apparent Michaelis-Menten constant (Kapp) was calculated as 3.04 mM. The fabricated biosensor also exhibited good repeatability, reproducibility, and storage stability. No interfering signals from dopamine, uric acid, ascorbic acid, paracetamol, folic acid, mannose, sucrose, and fructose were observed. The large electroactive surface area of carboxylated graphene oxide is a promising candidate for sensor preparation.

Decolorization of Rhodamine B by silver nanoparticle-loaded magnetic sporopollenin: characterization and process optimization.

Silver nanoparticles (Ag NPs) were reduced on the surface of magnetic sporopollenin (Fe3O4@SP) modified with poly-dopamine to enhance the degradation capability for Rhodamine B (RhB). The polydopamine-coated Fe3O4@SP (PDA@ Fe3O4@SP) acts as a self-reducing agent for Ag+ ions to Ag0. The structural properties of the synthesized nanocomposite were determined using Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and vibrating sample magnetometer (VSM). The systematic study of the degradation process was performed using Response Surface Methodology (RSM) to determine the relationship between the four process variables, namely, initial RhB concentration, NaBH4 amount, catalyst amount, and time. Optimum points were determined for these four parameters using both matrix and numerical optimization methods. Under optimum conditions, RhB was decolorized with a yield of 98.11%. The apparent activation energy (Ea) and rate constant (k) for the degradation were 24.13 kJ/mol and 0.77 min-1, respectively. The reusability studies of the Ag@PDA@Fe3O4@SP exhibited more than 85% degradation ability of the dye even after five cycles. As a result, Ag@PDA@Fe3O4@SP possessed high catalytic activity, fast reduction rate, good reusability, easy separation, and simple preparation, endowing this catalyst to be used as a promising catalyst for the decolorization of dyes in aqueous solutions.

A capillary driven microfluidic chip for SERS based hCG detection.

In this study, a capillary driven microfluidic chip-based immunoassay was developed for the determination of Human Chorionic Gonadotropin (hCG) protein, which is prohibited by the World Anti-Doping Agency (WADA). Here, we used antibody modified magnetic metal organic framework nanoparticles (MMOFs) as a capture prob in urine sample. MMOF captured hCG was transferred in a capillary driven microfluidic chip consisting of four chambers, and the interaction of MMOF with gold nanorods labelled with 5,5'-Dithiobis-(2-nitrobenzoic acid) (DTNB) as a Raman label was carried out in the capillary driven microfluidic chip. The movement of MMOF through first chamber to the last chamber was achieved with a simple magnet. In the last chamber of capillary driven microfluidic chip, SERS signals of DTNB molecules from the sandwich complex were recorded using a Raman spectrophotometer. The selectivity of the developed method was demonstrated by applying the same procedure for the detection of Human Luteinizing Hormone (hLH), Human Chorionic Gonadotropin Hormone (hGH) and Immunoglobulin G (IgG) protein. The regression coefficient and limit of detection obtained from the standard addition method were found as 0,9985 and 0,61 IU/L, respectively. Furthermore, the conventional ELISA method confirmed that the results obtained by the presented method were acceptable with the similarity of 97.9% in terms of average recovery value, for the detection of hCG in urine samples. The analysis system developed for target proteins will be an alternative technique such as Western Blot used in routine analysis that is expensive and time consuming.

Construction of a sensitive and selective plasmonic biosensor for prostate specific antigen by combining magnetic molecularly-imprinted polymer and surface-enhanced Raman spectroscopy.

Selective and sensitive detection of cancer biomarkers in serum samples is critical for early diagnosis of cancer. Prostate specific antigen is an important biomarker of prostate cancer, which ranks high among cancer-related deaths of men over 50 years old. Herein, a novel analytical method was introduced for detection of PSA by combining high selectivity of molecularly-imprinted polymers and high sensitivity of surface-enhanced Raman spectroscopy (SERS). Firstly, magnetic nanoparticles were grafted with an imprinted layer by using tannic acid as a functional monomer, diethylenetriamine as a cross-linker and prostate specific antigen as a template molecule. Detailed surface characterization and re-binding experiment results indicated that the imprinting of the antigen was successful with an imprinting factor of 5.58. The prepared magnetic molecularly imprinted polymers (MMIPs) were used as an antibody-free capture probe and labeled with gold nanoparticles that were modified with anti-PSA and a Raman reporter, namely 5,5'-dithiobis-(2-nitrobenzoic acid). Thus, a plasmonic structure (sandwich complex) was formed between MMIP and the SERS label. The limit of detection and limit of quantification of the designed sensor were 0.9 pg/mL and 3.2 pg/mL, respectively. The sensor also showed high recovery rates (98.0-100.1% for healthy person and 99.0-101.3% for patient) with low standard deviations (less than 4.3% for healthy person and less than 3.3% for patient) for PSA in serum samples. Compared with the traditional immunoassays, the proposed method has several advantages like low cost, reduced detection procedure, fast response, high sensitivity and selectivity. It is believed that the proposed method can be potentially used for selective and sensitive determination of tumor marker of prostate cancer in clinical applications.

A fluorescent artificial receptor with specific imprinted cavities to selectively detect colistin.

A novel and facile fluorescent artificial receptor on the basis of the molecularly imprinted polymer-coated graphene quantum dots was engineered successfully to detect colistin. The colistin imprinted graphene quantum dots (CMIP-GQDs) was synthesized by vinyl-based radical polymerization between functional monomers and crosslinker at around the template molecule on the surface of graphene quantum dots. The size of bare, CNIP-GQDs, and CMIP-GQDs was about 4.8 ± 0.6 nm, 18.4 ± 1.7 nm, and 19.7 ± 1.3 nm, respectively. The CMIP-GQDs, which showed the strong fluorescence emission at 440 nm with the excitation wavelength fixed at 380 nm, had excellent selectivity and specificity to rapidly recognize and detect colistin. The linear range of fluorescence quenching of this fluorescent artificial receptor for detection colistin was 0.016-2.0 µg mL-1 with a correlation coefficient (R2) of 0.99919, and the detection limit was 7.3 ng mL-1 in human serum samples. The designed receptor was successfully applied to detect colistin in human serum samples and it achieved excellent recoveries shifted from 93.8 to 105%. Graphical abstract.

Immunomagnetic separation and Listeriamonocytogenes detection with surface-enhanced Raman scattering

Background/aim: We aimed to develop a rapid method to enumerate Listeria monocytogenes (L. monocytogenes) utilizing magnetic nanoparticle based preconcentration and surface-enhanced Raman spectroscopy measurements. Materials and methods: Biological activities of magnetic Au-nanoparticles have been observed to have the high biocompatibility, and a sample immunosensor model has been designed to use avidin attached Au-nanoparticles for L. monocytogenes detection. Staphylococcus aureus (S. aureus) and Salmonella typhimurium (S. typhimurium) bacteria cultures were chosen for control studies. Antimicrobial activity studies have been done to identify bio-compatibility and bio-characterization of the Au-nanoparticles in our previous study and capturing efficiencies to bacterial surfaces have been also investigated. Results: We constructed the calibration graphs in various population density of L. monocytogenes as 2.2 × 101 to 2.2 × 106 cfu/mL and the capture efficiency was found to be 75%. After the optimization procedures, population density of L. monocytogenes and Raman signal intensity showed a good linear correlation (R2 = 0.991) between 102 to 106 cfu/mL L. monocytogenes. The presented sandwich assay provides low detection limits and limit of quantification as 12 cfu/mL and 37 cfu/mL, respectively. We also compared the experimental results with reference plate-counting methods and the practical utility of the proposed assay is demonstrated using milk samples. Conclusion: It is focused on the enumeration of L. monocytogenes in milk samples and the comparision of results of milk analysis obtained by the proposed SERS method and by plate counting method stay in food agreement. In the present study, all parameters were optimized to select SERS-based immunoassay method for L. monocytogenes bacteria to ensure LOD, selectivity, precision and repeatablity.

Synthesis of magnetic halloysite nanotube-based molecularly imprinted polymers for sensitive spectrophotometric detection of metoclopramide in urine samples.

A novel molecularly imprinted polymer was synthesized on magnetic halloysite nanotube via surface initiated reversible addition-fragmentation chain transfer polymerization in the presence of 2-aminoethylmethacrylamide, 2-Cyano-2-propyl benzodithioate, ethylene glycol dimethacrylate (EGDMA) and azobis(isobutyronitrile) for sensitive and selective spectrophotometric determination of metoclopramide in urine samples. The synthesized imprinted polymer was characterized by several surface characterization techniques and the results indicated there was a thin polymer network on the magnetic halloysite nanotube. The rebinding properties of the molecularly imprinted magnetic halloysite nanotube were also investigated in detail and the maximum adsorption capacity and imprinting factor were found to be 37.8 mg/g and 4.51, respectively. The application of the proposed method was carried out by enrichment and spectrophotometric determination of metoclopramide via formation of a charge transfer complex between picric acid and eluted metoclopramide. Under the optimized conditions, the calibration curve was linear in the concentration range of 5.0-150.0 ng/mL and the limit of detection and the limit of quantification were calculated to be 1.5 ng/mL and 4.95 ng/mL, respectively. The inter-day and intra-day precisions were below 5% and recoveries were between 92.8% and 99.2%. The results showed that the proposed method increased the sensitivity and selectivity for spectrophotometric determination of metoclopramide.

Magnetic nanoparticles coated with aminated polymer brush as a novel material for effective removal of Pb(II) ions from aqueous environments.

In the present study, a poly (vinylbenzyl chloride) grafted Fe3O4 nanoparticle (Fe3O4@PVBC) was prepared by surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization and subsequently coated with tris (aminoethyl) amine (TAEA). Then, Fe3O4@PVBC-TAEA nanoparticles were utilized as a novel adsorbent for removal of Pb(II) from aqueous media and optimal adsorption conditions were determined with response surface methodology (RSM). The used adsorbent was characterized by using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). RSM with central composite design (CCD) was carried out to evaluate the effect of initial pH, initial Pb(II) concentration (C0, mg/L), adsorbent dosage (mg), and contact time (min). The optimum initial pH, C0, adsorbent dosage, and contact time were found to be 5.88, 46.51 mg/L, 17.41 mg, and 108.21 min, respectively. The maximum removal efficiency and adsorption capacity were 97.07% and 129.65 mg/g under these conditions, respectively. The kinetic data revealed that the adsorption mechanism could be best explained by the pseudo-second-order and Weber-Morris models. The isotherm studies found that both the Langmuir and Freundlich isotherm models fitted the experimental data well. The thermodynamic analysis indicated that the adsorption nature is exothermic, applicable, and spontaneous.

Selective separation and determination of quercetin from red wine by molecularly imprinted nanoparticles coupled with HPLC and ultraviolet detection.

In this study, a highly sensitive and selective sample pretreatment procedure using molecularly imprinted silica nanoparticles was developed for the extraction and determination of quercetin in red wine samples coupled with high-performance liquid chromatography with ultraviolet detection. The imprinted silica nanoparticles were prepared in the presence of N-acryoyl-l-aspartic acid (functional monomer), quercetin (template), azobisisobutyronitrile (initiator) and methylene bisacrylamide (cross-linker) and methanol/water (porogen) via surface-initiated reversible addition-fragmentation chain transfer polymerization. Surface characterization was performed and several imprinting parameters were investigated, and the results indicated that adsorption of quercetin on the imprinted silica nanoparticles followed a pseudo-first-order adsorption isotherm with a maximum adsorption capacity at 26.4 mg/g within 60 min. The imprinted silica nanoparticles also showed satisfactory selectivity towards quercetin as compared with its structural analogues. Moreover, the imprinted nanoparticles preserved their recognition ability even after five adsorption-desorption cycles. Meanwhile, the nanoparticles were successfully applied to selective extraction of quercetin from red wine with a high recovery (99.7-100.4%). The limit of detection was calculated to be 0.058 µg/mL with a correlation coefficient 0.9996 in the range of 0.2-50 µg/mL. As a result, the developed selective extraction method using molecular imprinting technology simplifies the sample pretreatment procedure before determination of quercetin in real samples.

Efficient and selective separation of metronidazole from human serum by using molecularly imprinted magnetic nanoparticles.

Magnetic molecularly imprinted nanoparticles were prepared through surface-initiated reversible addition fragmentation chain transfer polymerization by using metronidazole as a template. The molecularly imprinted magnetic nanoparticles were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, and vibrating sample magnetometry. The adsorption characteristics were also investigated and the kinetics of the adsorption of metronidazole on the imprinted nanoparticles were described by the second-order kinetic model with the short equilibrium adsorption time (30 min). The adsorption isotherm was well matched with the Langmuir isotherm in which the maximum adsorption capacity was calculated to be 40.1 mg/g. Furthermore, the imprinted magnetic nanoparticles showed good selectivity as well as reusability even after six adsorption-desorption cycles. The imprinted magnetic nanoparticles were used as a sorbent for the selective separation of metronidazole from human serum. The recoveries of metronidazole from human serum changed between 97.5 and 99.8% and showed similar sensitivity as an enzyme-linked immunoassay method. Therefore, the molecularly imprinted magnetic nanoparticles might have potential application for the selective and reliable separation of metronidazole from biological fluids in clinical applications.

A novel route to prepare a multilayer system via the combination of interface-mediated catalytic chain transfer polymerization and thiol-ene click chemistry.

Herein, we have designed a novel multilayer system composed of poly(methyl methacrylate) [poly(MMA)] brush, biotin, streptavidin and protein-A on a silicon substrate to attach onanti-immunoglobulin G (anti-IgG). poly(MMA) brush with vinyl end-group was first synthesized by the interface-mediated catalytic chain transfer polymerization. The brush was then modified with cysteamine molecules to generate the polymer chains with amine end-group via a thiol-ene click chemistry. The amine end-groups of poly(MMA) chains were also modified with biotin units to ensure selective connection points for streptavidin molecules. Finally, a multilayer system on the silicon substrate was formed by using streptavidin and protein-A molecules, respectively. This multilayer system was employed to attach anti-IgG molecules in a highly oriented manner and provide anti-IgG molecular functional configuration on the multilayer. High reproducibility of the amount of anti-IgG adsorption and homogeneous anti-IgG adsorption layer on the silicon surface could be provided by this multilayer system. The multilayer system with protein A may be opened the door for designing an efficient immunoassay protein chip.

Quantitative Characterization of Magnetic Mobility of Nanoparticle in Solution-Based Condition.

Magnetic nanoparticles are considered as the ideal substrate to selectively isolate target molecules or organisms from sample solutions in a wide variety of applications including bioassays, bioimaging and environmental chemistry. The broad array of these applications in fields requires the accurate magnetic characterization of nanoparticles for a variety of solution based-conditions. Because the freshly synthesized magnetic nanoparticles demonstrated a perfect magnetization value in solid form, they exhibited a different magnetic behavior in solution. Here, we present simple quantitative method for the measurement of magnetic mobility of nanoparticles in solution-based condition. Magnetic mobility of the nanoparticles was quantified with initial mobility of the particles using UV-vis absorbance spectroscopy in water, ethanol and MES buffer. We demonstrated the efficacy of this method through a systematic characterization of four different core-shell structures magnetic nanoparticles over three different surface modifications. The solid nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD) and saturation magnetization (Ms). The surfaces of the nanoparticles were functionalized with 11-mercaptoundecanoic acid and bovine serum albumin BSA was selected as biomaterial. The effect of the surface modification and solution media on the stability of the nanoparticles was monitored by zeta potentials and hydrodynamic diameters of the nanoparticles. Results obtained from the mobility experiments indicate that the initial mobility was altered with solution media, surface functionalization, size and shape of the magnetic nanoparticle. The proposed method easily determines the interactions between the magnetic nanoparticles and their surrounding biological media, the magnetophoretic responsiveness of nanoparticles and the initial mobilities of the nanoparticles.

A new plasmonic device made of gold nanoparticles and temperature responsive polymer brush on a silicon substrate.

This paper reports a general stepwise route assembling interface-mediated RAFT polymerization of 2-methoxyethoxy ethyl methacrylate and conversion of dodecyl trithiocarbonate end groups to thiol groups for gold nanoparticle assemblies. We intended by this way a new plasmonic device made of gold nanoparticles (Au NPs) and temperature responsive [poly((2-methoxyethoxy)ethyl) methacrylate] [poly(MEO2-MA)] brush on a silicon substrate. This polymeric layer replies to temperature changing by conformational variation and is therefore able to change the distance between the Au NPs on the brush layer with 5,5-dithiobis(2-dinitrobenzoic acid) (DTNB). We show that an increment of the external temperature reversibly stimulates a significant increase of the DTNB SERS signal.

Fabrication of a SERS based aptasensor for detection of ricin B toxin.

In this report, we have developed a novel surface-enhanced Raman scattering (SERS) aptasensor for ricin B toxin recognition based on Ag nanoparticles labeled with 4,4'-bipyridyl (Bpy, Raman reporter) and ricin B aptamer. The hybrid silicon substrate was first prepared via surface-mediated RAFT polymerization of N-acryoyl-l-valine in the presence of 2-(butylthio-carbonothioylthio)-2-methylpropionic acid-modified silicon wafer as a RAFT agent and then biofunctionalized with ricin B aptamer. In this novel system, the ricin B aptamer functionalized silicon substrate was used as a scavenger for target ricin B molecules. After ricin B molecules were separated from the matrix, the sandwich assay procedure was applied using Ag nanoparticles labeled with Bpy and ricin B aptamer which act as SERS probes. Meanwhile, to enhance the SERS signal, silver deposition on the sandwich complex was also performed. The correlation between the ricin B concentration and SERS signal was found to be linear within the range of 1.0 fM to 50 pM. The limit of detection for the SERS aptasensor was determined as 0.32 fM. Furthermore, the SERS aptasensor was also evaluated for detecting ricin B in artificially contaminated orange juice, milk, blood and urine. Finally, this method has the potential to be used for the detection of other protein toxins in a complex matrix if a specific aptamer for that protein toxin can be designed.

Extremely sensitive sandwich assay of kanamycin using surface-enhanced Raman scattering of 2-mercaptobenzothiazole labeled gold@silver nanoparticles.

Herein, we report the development of extremely sensitive sandwich assay of kanamycin using a combination of anti-kanamycin functionalized hybrid magnetic (Fe3O4) nanoparticles (MNPs) and 2-mercaptobenzothiazole labeled Au-core@Ag-shell nanoparticles as the recognition and surface-enhanced Raman scattering (SERS) substrate, respectively. The hybrid MNPs were first prepared via surface-mediated RAFT polymerization of N-acryloyl-L-glutamic acid in the presence of 2-(butylsulfanylcarbonylthiolsulfanyl) propionic acid-modified MNPs as a RAFT agent and then biofunctionalized with anti-kanamycin, which are both specific for kanamycin and can be collected via a simple magnet. After separating kanamycin from the sample matrix, they were sandwiched with the SERS substrate. According to our experimental results, the limit of detection (LOD) was determined to be 2pg mL(-1), this value being about 3-7 times more than sensitive than the LOD of previously reported results, which can be explained by the higher SERS activity of silver coated gold nanoparticles. The analysis time took less than 10min, including washing and optical detection steps. Furthermore, the sandwich assay was evaluated for investigating the kanamycin specificity on neomycin, gentamycin and streptomycin and detecting kanamycin in artificially contaminated milk.

Fragmented proteins as food emulsion stabilizers: A theoretical study.

Using a model based on the primary structure of αs1 -casein, the colloid stabilizing ability of fragmented protein and that of the intact chains are compared. We perform self consistent field (SCF) calculations to obtain the induced interaction potentials between the oil droplets, resulting from the overlap of adsorbed protein layers in each case. For the intact αs1 -casein, we confirm the known result, that the mediated interparticle interaction potential develops a deep attractive energy minimum at high salt concentrations and pH values close to the isoelectric point of the protein. The same does not occur for the appropriately fragmented systems, with improved emulsion stability predicted as a result, even at pH values close to pI. It is shown that this superior performance, for the case considered, is due to the diblock-type behavior of one of the fragments. However, it is well known that αs1 -casein more closely resembles the less favorable triblock structure. However, it is also demonstrated that the presence of a "diblock" like fragment by itself may not always be enough to produce a better emulsion stabilizer. It is seen that the hydrolysis of some peptide bonds may indeed lead to a suitable polypeptide, but that this is displaced from the interface by the structurally less desirable ones, also generated by the fragmentation process. The displacement occurs due to the competitive adsorption between different fragments. The removal of the undesirable fragments from the solution is found to greatly enhance the predicted colloid stabilizing ability of the remaining polypeptide.

Molecularly imprinted superparamagnetic iron oxide nanoparticles for rapid enrichment and separation of cholesterol.

A general protocol to prepare surface molecularly imprinted polymer core-shell superparamagnetic Fe3O4 nanoparticles (Fe3O4@MIP SPNPs), using a surface-mediated RAFT polymerization approach, is described. Cholesterol-imprinted Fe3O4@MIP SPNPs were obtained by oleic acid-stabilized Fe3O4 nanoparticles with a trithiocarbonate agent and subsequently by polymerizing thin molecularly imprinted layers composed of dimethylacrylamide and N,N'-methylene(bis)acrylamide units. The surface-mediated RAFT polymerization approach allows the synthesis of ∼20 nm hybrid composite particles with a ∼6 nm MIP shell, exhibiting superparamagnetic properties (saturation magnetization = 35.4 emu g(-1)) and specific molecular recognition of cholesterol. The Fe3O4@MIP SPNPs show the capability of rapid enriching and separating cholesterol (∼3.1% in weight) and are renewable and cyclically exploited due to their monodispersive and superparamagnetic features. Moreover, under optimal conditions, the Fe3O4@MIP SPNP recoveries of spiked human serum, milk, yolk and beef were 91.6%, 93.6%, 92.4% and 91.2%, respectively. Finally, the method of molecular imprinting on superparamagnetic particles can be extended to a wide range of applications for cell sorting, biomolecule enrichment and separation, and drug delivery.

A SERS-based sandwich assay for ultrasensitive and selective detection of Alzheimer's tau protein.

In this study, a simple and highly selective homogeneous sandwich assay was developed for fast and ultrasensitive detection of the tau protein using a combination of monoclonal antitau functionalized hybrid magnetic nanoparticles and polyclonal antitau immobilized gold nanoparticles as the recognition and surface-enhanced Raman scattering (SERS) component, respectively. The magnetic silica particles were first coated with poly(2-hydroxyethyl methacrylate) via surface-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization and then biofunctionalized with monoclonal antitau, which are both specific for tau and can be collected via a simple magnet. After separating tau from the sample matrix, they were sandwiched with the SERS substrate composed of polyclonal antitau and 5,5-dithiobis(2-dinitrobenzoic acid) on gold nanoparticles. The correlation between the tau concentration and SERS signal was found to be linear within the range of 25 fM to 500 nM. The limit of detection for the sandwich assay is less than 25 fM. Moreover, the sandwich assay was also evaluated for investigating the tau specificity on bovine serum albumin and immunoglobulin G.