Nanoceria-based lateral flow immunoassay for hydrogen peroxide-free colorimetric biosensing for C-reactive protein.

During the recent several decades, lateral flow immunoassay (LFIA) constructed with gold nanoparticle (AuNP) has been widely utilized to conveniently detect target analyte. However, AuNP-based LFIA has limitations, such as limited detection sensitivity and quantification capability. Herein, to overcome these constraints, we have developed cerium oxide nanoparticle (nanoceria)-based LFIA for C-reactive protein (CRP) detection in human serum samples. It was fabricated with nanoceria, a notable nanozyme that shows an oxidase activity to quickly oxidize organic substrate, such as 3,3',5,5'-tetramethylbenzidine (TMB), to produce colored product without any oxidizing agent (e.g., hydrogen peroxide), which is advantageous for realizing point-of-care testing (POCT) applications. By employing human blood serum spiked with CRP, the nanoceria-based LFIA showed two blue-colored lines on the test and control region within 3 min via TMB oxidation, by the captured nanoceria through antigen-antibody interaction. The produced blue-colored lines were distinguished by naked eyes and quantitated with real images acquired by a conventional smartphone with the ImageJ software. With this strategy, target CRP was specifically determined down to 117 ng mL-1 with high detection precisions yielding coefficient of variation of 9.8-11.3% and recovery of 90.7-103.2% using human blood serum samples. This investigation demonstrates the potential of oxidase-like nanoceria for developing LFIA, which is particularly useful in instrumentation-free POCT environments.

Colorimetric determination of phenolic compounds using peroxidase mimics based on biomolecule-free hybrid nanoflowers consisting of graphitic carbon nitride and copper.

Hybrid nanoflowers consisting of graphitic carbon nitride (GCN) and copper were successfully constructed without the involvement of any biomolecule, by simply mixing them at room temperature to induce proper self-assembly to achieve a flower-like morphology. The resulting biomolecule-free GCN-copper hybrid nanoflowers (GCN-Cu NFs) exhibited an apparent peroxidase-mimicking activity, possibly owing to the synergistic effect from the coordination of GCN and copper, as well as their large surface area, which increased the number of catalytic reaction sites. The peroxidase-mimicking GCN-Cu NFs were then employed in the colorimetric determination of selected phenolic compounds hydroquinone (HQ), methylhydroquinone (MHQ), and catechol (CC). For samples without phenolic compounds, GCN-Cu NFs catalyzed the oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2, producing an intense blue color signal. Conversely, in the presence of phenolic compounds, the oxidation of TMB was inhibited, resulting in a significant reduction of the color signal. Using this strategy, HQ, MHQ, and CC were selectively and sensitively determined in a linear range up to 100 µM with detection limits down to 0.82, 0.27, and 0.36 µM, respectively. The practical utility of this assay system was also validated by using it to detect phenolic compounds spiked in tap water, yielding a good recovery of 97.1-108.9% and coefficient of variation below 3.0%, demonstrating the excellent reliability and reproducibility of this strategy. Colorimetric determination of phenolic compounds using peroxidase mimics based on biomolecule-free hybrid nanoflowers consisting of graphitic carbon nitride and copper.

Rosette-shaped graphitic carbon nitride acts as a peroxidase mimic in a wide pH range for fluorescence-based determination of glucose with glucose oxidase.

Rosette-shaped graphitic carbon nitride (rosette-GCN) is described as a promising alternative to natural peroxidase for its application to fluorescence-based glucose assays. Rosette-GCN was synthesized via a rapid reaction between melamine and cyanuric acid for 10 min at 35 °C, followed by thermal calcination for 4 h. Importantly, rosette-GCN possesses a peroxidase-like activity, producing intense fluorescence from the oxidation of Amplex UltraRed in the presence of H2O2 over a broad pH-range of, including neutral pH; the peroxidase activity of rosette-GCN was ~ 10-fold higher than that of conventional bulk-GCN. This enhancement of peroxidase activity is presumed to occur because rosette-GCN has a significantly larger surface area and higher porosity while preserving its unique graphitic structure. Based on the high peroxidase activity of rosette-GCN along with the catalytic action of glucose oxidase (GOx), glucose was reliably determined down to 1.2 µM with a dynamic linear concentration range of 5.0 to 275.0 µM under neutral pH conditions. Practical utility of this strategy was also successfully demonstrated by determining the glucose levels in serum samples. This work highlights the advantages of GCNs synthesized via rapid methods but with unique structures for the preparation of enzyme-mimicking catalysts, thus extending their applications to the diagnostics field and other biotechnological fields. Graphical abstract.

Erratum: Cuvette-Type LSPR Sensor for Highly Sensitive Detection of Melamine in Infant Formulas. Sensors 2018, 19(18), 3839.

The authors wish to make the following erratum to this paper [...].

Cuvette-Type LSPR Sensor for Highly Sensitive Detection of Melamine in Infant Formulas.

The globalization of food distribution has made necessary to secure safe products to the general consumers through the rapid detection of harmful additives on the field. For this purpose, we developed a cuvette-type localized surface plasmon resonance (LSPR) sensor that can be easily used by consumers with conventional ultraviolet-visible light spectrophotometer for in-situ measurements. Gold nanoparticles were uniformly deposited on a transparent substrate via a self-assembly method to obtain a plasmonically active chip, and the chemical receptor p-nitroaniline (p-NA) was functionalized to stabilize the device sensitivity under external temperature and pH conditions. The fabricated chip was fixed onto a support and combined with a cuvette-type LSPR sensor. To evaluate the applicability of this sensor on the field, sensitivity and quantitative analysis experiments were conducted onto melamine as a model sample from harmful food additives. Under optimal reaction condition (2 mM p-NA for 20 min), we achieved an excellent detection limit (0.01 ppb) and a dynamic range allowing quantitative analysis over a wide concentration range (0.1-1000 ppb) from commercially available milk powder samples.

Cell-based method utilizing fluorescent Escherichia coli auxotrophs for quantification of multiple amino acids.

A cell-based assay system for simultaneous quantification of the three amino acids, phenylalanine (Phe), methionine (Met), and leucine (Leu) in a single biological sample, was developed and applied in the multiplex diagnosis of three key metabolic diseases of newborn babies. The assay utilizes three Escherichia coli auxotrophs, which grow only in the presence of the corresponding target amino acids and which contain three different fluorescent reporter plasmids that produce distinguishable fluorescence signals (red, green, and cyan) in concert with cell growth. To mixtures of the three auxotrophs, immobilized on agarose gels arrayed on a well plate, is added a test sample. Following incubation, the concentrations of the three amino acids in the sample are simultaneously determined by measuring the intensities of three fluorescence signals that correspond to the reporter plasmids. The clinical utility of this assay system was demonstrated by employing it to identify metabolic diseases of newborn babies through the quantification of Phe, Met, and Leu in clinically derived dried blood spot specimens. The general strategy developed in this effort should be applicable to the design of new assay systems for the quantification of multiple amino acids derived from complex biological samples and, as such, to expand the utilization of cell-based analytical systems that replace conventional, yet laborious methods currently in use.

Surface display of recombinant proteins on Escherichia coli by BclA exosporium of Bacillus anthracis.

BACKGROUND: The anchoring motif is one of the most important aspects of cell surface display as well as efficient and stable display of target proteins. Thus, there is currently a need for the identification and isolation of novel anchoring motifs. RESULTS: A system for the display of recombinant proteins on the surface of Escherichia coli was developed using the Bacillus anthracis exosporal protein (BclA) as a new anchoring motif. For the surface display of recombinant proteins, the BAN display platform was constructed in which a target protein is linked to the C-terminus of N-terminal domain (21 amino acids) of BclA. The potential application of BAN platform for cell surface display was demonstrated with two model proteins of different size, the Bacillus sp. endoxylanase (XynA) and monooxygenase (P450 BM3m2). Through experimental analysis including outer membrane fractionation, confocal microscopy and activity assay, it was clearly confirmed that both model proteins were successfully displayed with high activities on the E. coli cell surface. CONCLUSIONS: These results of this study suggest that the strategy employing the B. anthracis BclA as an anchoring motif is suitable for the display of heterologous proteins on the surface of E. coli and consequently for various biocatalytic applications as well as protein engineering.

Label-free electrochemical diagnosis of viral antigens with genetically engineered fusion protein.

We have developed a simple electrochemical biosensing strategy for the label-free diagnosis of hepatitis B virus (HBV) on a gold electrode surface. Gold-binding polypeptide (GBP) fused with single-chain antibody (ScFv) against HBV surface antigen (HBsAg), in forms of genetically engineered protein, was utilized. This GBP-ScFv fusion protein can directly bind onto the gold substrate with the strong binding affinity between the GBP and the gold surface, while the recognition site orients toward the sample for target binding at the same time. Furthermore, this one-step immobilization strategy greatly simplifies a fabrication process without any chemical modification as well as maintaining activity of biological recognition elements. This system allows specific immobilization of proteins and sensitive detection of targets, which were verified by surface plasmon resonance analysis and successfully applied to electrochemical cyclic voltammetry and impedance spectroscopy upto 0.14 ng/mL HBsAg.

Development of a plastic-based microfluidic immunosensor chip for detection of H1N1 influenza.

Lab-on-a-chip can provide convenient and accurate diagnosis tools. In this paper, a plastic-based microfluidic immunosensor chip for the diagnosis of swine flu (H1N1) was developed by immobilizing hemagglutinin antigen on a gold surface using a genetically engineered polypeptide. A fluorescent dye-labeled antibody (Ab) was used for quantifying the concentration of Ab in the immunosensor chip using a fluorescent technique. For increasing the detection efficiency and reducing the errors, three chambers and three microchannels were designed in one microfluidic chip. This protocol could be applied to the diagnosis of other infectious diseases in a microfluidic device.

Development of a Cuvette-Based LSPR Sensor Chip Using a Plasmonically Active Transparent Strip.

This research demonstrates the development of a transmission-mode localized surface plasmon resonance (LSPR) sensor chip using a cuvette cell system for the sensitive detection of a biomolecule marker such as C-reactive protein (CRP). In order to develop a highly sensitive LSPR sensor chip, plasmonically active gold nanoparticles (AuNPs) were decorated onto various transparent substrates in the form of a uniform, high-density single layer using a self-assembly process. The transparent substrate surface was modified with amine functional groups via (3-Aminopropyl)triethoxysilane (APTES) treatment, and the ligand concentration and temperature (0.5% APTES at 60°C) were then optimized to control the binding energy with AuNPs. The optimized plasmonically active strip was subsequently prepared by dipping the amine-functionalized substrate into AuNPs for 8 h. The optimized plasmonic strip functionalized with anti-CRP was transformed into a portable LSPR sensor chip by placing it inside a cuvette cell system, and its detection performance was evaluated using CRP as a model sample. The detection limit for CRP using our LSPR sensor chip was 0.01 µg/mL, and the detection dynamic range was 0.01-10 µg/mL with a %CV of <10%, thus confirming its selectivity and good reproducibility. These findings illustrate that the highly sensitive portable LSPR biosensor developed in this study is expected to be widely used in a diverse range of fields such as diagnosis, medical care, environmental monitoring, and food quality control.

Shape-controlled assemblies of graphitic carbon nitride polymer for efficient sterilization therapies of water microbial contamination via 2D g-C3N4 under visible light illumination.

Bacterial pathogens of water origin have potential public threats thus suggesting the need of developing efficient and sustainable water disinfection strategies from waterborne pathogens. We set out to synthesize different controlled morphologies of graphitic carbon nitride (g-C3N4) polymer, evaluate their comparative effects on the generation of reactive oxygen species (ROS), and investigate potential applications in water purification systems. Characterization of the synthesized microstructures of g-C3N4, such as melamine-cyanuric acid (MCA)-based rosette-type, rod-type, 2D hexagonal, and 3D cubic mesoporous silica was accomplished using Fourier transform infrared (FT-IR), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The microbial inhibitory potential of 2D g-C3N4 photocatalyst against waterborne Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium was evaluated based on the effective activity of 2D g-C3N4 upon visible light excitations. The microbicidal efficiency of 2D g-C3N4 was evident within 30 min of visible light exposure via direct interaction, while other microstructures of g-C3N4 demonstrated only slight antimicrobial effects after 120 min, with insufficient ROS generation. The antimicrobial and ROS-generating effects of 2D g-C3N4 depended on the type and surface area of the synthesized 2D g-C3N4 material. Considering its availability and excellent disinfection activity, 2D g-C3N4 obtained from simple and convenient facile synthesis is a promising solar-driven photocatalyst for clearing microbial contamination from water.

Selection of affinity peptides for interference-free detection of cholera toxin.

Cholera toxin is a major virulent agent of Vibrio cholerae, and it can rapidly lead to severe dehydration, shock, causing death within hours without appropriate clinical treatments. In this study, we present a method wherein unique and short peptides that bind to cholera toxin subunit B (CTX-B) were selected through M13 phage display. Biopanning over recombinant CTX-B led to rapid screening of a unique peptide with an amino acid sequence of VQCRLGPPWCAK, and the phage-displayed peptides analyzed using ELISA, were found to show specific affinities towards CTX-B. To address the use of affinity peptides in development of the biosensor, sequences of newly selected peptides were modified and chemically synthesized to create a series of affinity peptides. Performance of the biosensor was studied using plasmonic-based optical techniques: localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS). The limit of detection (LOD) obtained by LSPR with 3σ-rule was 1.89ng/mL, while SERS had a LOD of 3.51pg/mL. In both cases, the sensitivity was much higher than the previously reported values, and our sensor system was specific towards actual CTX-B secreted from V. cholera, but not for CTX-AB5.

Heteroassembled gold nanoparticles with sandwich-immunoassay LSPR chip format for rapid and sensitive detection of hepatitis B virus surface antigen (HBsAg).

This study aimed to develop a more sensitive method for the detection of hepatitis B surface antigen (HBsAg) using heteroassembled gold nanoparticles (AuNPs). A single layered localized surface plasmon resonance (LSPR) chip format was developed with antigen-antibody reaction-based detection symmetry using AuNPs, which detected HBsAg at 10 pg/mL. To further improve the detection limit, a modified detection format was fabricated by fixing a secondary antibody (to form a heteroassembled sandwich format) to the AuNP monolayer, which enhanced the detection sensitivity by about 100 times. The developed heteroassembled AuNPs sandwich-immunoassay LSPR chip format was able to detect as little as 100 fg/mL of HBsAg within 10-15 min. In addition, the heteroassembled AuNPs sandwich-immunoassay LSPR chip format did not show any non-specific binding to other tested antigens, including alpha fetoprotein (AFP), C-reactive protein (CRP), and prostate-specific antigen (PSA). These findings confirm that the proposed detection strategy of heteroassembled AuNPs sandwich-immunoassay LSPR chip format may provide a new platform for early diagnosis of various human diseases.

Visible-light-driven dynamic cancer therapy and imaging using graphitic carbon nitride nanoparticles.

Organic graphitic carbon nitride nanoparticles (NP-g-CN), less than 30 nm in size, were synthesized and evaluated for photodynamic therapy (PDT) and cell imaging applications. NP-g-CN particles were prepared through an intercalation process using a rod-like melamine-cyanuric acid adduct (MCA) as the molecular precursor and a eutectic mixture of LiCl-KCl (45:55 wt%) as the reaction medium for polycondensation. The nano-dimensional NP-g-CN penetrated the malignant tumor cells with minimal hindrance and effectively generated reactive oxygen species (ROS) under visible light irradiation, which could ablate cancer cells. When excited by visible light irradiation (λ > 420 nm), NP-g-CN introduced to HeLa and cos-7 cells generated a significant amount of ROS and killed the cancerous cells selectively. The cytotoxicity of NP-g-CN was manipulated by altering the light irradiation and the BP-g-CN caused more damage to the cancer cells than normal cells at low concentrations. As a potential non-toxic organic nanomaterial, the synthesized NP-g-CN are biocompatible with less cytotoxicity than toxic inorganic materials. The combined effects of the high efficacy of ROS generation under visible light irradiation, low toxicity, and bio-compatibility highlight the potential of NP-g-CN for PDT and imaging without further modification.

Porous NH2-MIL-125 as an efficient nano-platform for drug delivery, imaging, and ROS therapy utilized Low-Intensity Visible light exposure system.

Metal-organic frameworks are a novel class of organic-inorganic hybrid polymer with potential applications in bioimaging, drug delivery, and ROS therapy. NH2-MIL-125, which is a titanium-based metal organic framework with a large surface area of 1540m2/g, was synthesized using a hydrothermal method. The material was characterized by powder X-ray diffreaction (PXRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM), and N2 isotherm analyses. The size of the polymer was reduced to the nanoscale using a high-frequency sonication process. PEGylation was carried out to improve the stability and bioavailability of the NMOF. The as-synthesized nano-NH2-MIL-125/PEG (NMOF/PEG) exhibited good biocompatibility over the (Cancer) MCF-7 and (Normal) COS-7 cell line. The interaction of NMOF/PEG with the breast cancer cell line (MCF-7) was examined by BIO-TEM analysis and laser confocal imaging. 2',7'-dichlorofluorescin diacetate (DCFDA) analysis confirmed that NMOF/PEG produced free radicals inside the cancer cell line (MCF-7) upon visible light irradiation. NMOF/PEG absorbed a large amount of DOX (20wt.% of DOX) and showed pH, and photosensitive release. This controlled drug delivery was attributed to the presence of NH2, Ti group in MOF and a hydroxyl group in PEG. This combination of chemo- and ROS-therapy showed excellent efficiency in killing cancer MCF-7 cells.

Development of gold nanoparticle-aptamer-based LSPR sensing chips for the rapid detection of Salmonella typhimurium in pork meat.

A non-labeled, portable plasmonic biosensor-based device was developed to enable the ultra-sensitive and selective detection of Salmonella typhimurium in pork meat samples. Specifically, a plasmonic sensor, using the self-assembly of gold nanoparticles (AuNPs) to achieve a regulated diameter of 20 nm for the AuNP monolayers, was used to conduct high-density deposition on a transparent substrate, which produced longitudinal wavelength extinction shifts via a localized surface plasmon resonance (LSPR) signal. The developed aptamers conjugated to the LSPR sensing chips revealed an ultra-sensitive upper limit of detection (LOD) of approximately 104 cfu/mL for S. typhimurium in pure culture under the optimal assay conditions, with a total analysis time of 30-35 min. When the LSPR sensing chips were applied on artificially contaminated pork meat samples, S. typhimurium in the spiked pork meat samples was also detected at an LOD of 1.0 × 104 cfu/mL. The developed method could detect S. typhimurium in spiked pork meat samples without a pre-enrichment step. Additionally, the LSPR sensing chips developed against S. typhimurium were not susceptible to any effect of the food matrix or background contaminant microflora. These findings confirmed that the developed gold nanoparticle-aptamer-based LSPR sensing chips could facilitate sensitive detection of S. typhimurium in food samples.

Cesium-induced inhibition of bacterial growth of Pseudomonas aeruginosa PAO1 and their possible potential applications for bioremediation of wastewater.

Radioactive isotopes and fission products have attracted considerable attention because of their long lasting serious damage to the health of humans and other organisms. This study examined the toxicity and accumulation behavior of cesium towards P. aeruginosa PAO1 and its capacity to remove cesium from waste water. Interestingly, the programmed bacterial growth inhibition occurred according to the cesium environment. The influence of cesium was analyzed using several optical methods for quantitative evaluation. Cesium plays vital role in the growth of microorganisms and functions as an anti-microbial agent. The toxicity of Cs to P. aeruginosa PAO1 increases as the concentration of cesium is increased in concentration-dependent manner. P. aeruginosa PAO1 shows excellent Cs removal efficiency of 76.1% from the contaminated water. The toxicity of cesium on the cell wall and in the cytoplasm were studied by transmission electron microscopy and electron dispersive X-ray analysis. Finally, the removal of cesium from wastewater using P. aeruginosa PAO1 as a potential biosorbent and the blocking of competitive interactions of other monovalent cation, such as potassium, were assessed. Overall, P. aeruginosa PAO1 can be used as a high efficient biomaterial in the field of radioactive waste disposal and management.

Porous Covalent Triazine Polymer as a Potential Nanocargo for Cancer Therapy and Imaging.

A microporous covalent triazine polymer (CTP) network with a high surface area was synthesized via the Friedel-Crafts reaction and employed as a potential transport system for drug delivery and controlled release. The CTP was transformed to the nanoscale region by intense ultrasonication followed by filtration to yield nanoscale CTP (NCTP). This product showed excellent dispersibility in physiological solution while maintaining its chemical structure and porosity. An anticancer drug, doxorubicin (DOX), was loaded onto the NCTP through hydrophobic and π-π interactions, and its release was controlled at pH 4.8 and 7.4. The NCTP showed no toxicity toward cancer or normal cells, but the NCTP-DOX complex showed high efficacy against both types of cells in vitro. In-vitro cell imaging revealed that NCTP is a potential material for bioimaging. The potency of NCTP on cellular senescence was confirmed by the expression of senescence associated marker proteins p53 and p21. These results suggest that NCTP can be used as a new platform for drug delivery and imaging with potential applications in diagnosis and therapy.

Microbial inactivation and pesticide removal by remote exposure of atmospheric air plasma in confined environments.

Microbial inactivation and pesticide removal by remote exposure of atmospheric air plasma were investigated in confined environments, including an airtight box and commercial refrigerator. The relative sterilization ratios of remote plasma exposure in an airtight box were found to be affected by the distance from the plasma generator, the volume of box and the time of irradiation; however, over 99% saturation was obtained within only 120 s in all experiments. The sterilization of microorganisms and the removal of pesticide in a refrigerator with a volume of 292 l were also successfully achieved, resulting in over 99% inactivation or decontamination in a few minutes. Considering the reported results by direct plasma exposure and circulation, it can be concluded that the confined environment enhances the efficient irradiation of plasma by eliminating air flow. This system can be applied to the storage to keep agricultural products freshly and exclusion of harmful materials on the products.