The diagnosis of gout was developed through the detection of monosodium urate (MSU) crystals in the synovial fluid of patients with gout using MSU-binding peptides. Amino acid sequences with a high binding affinity to MSU crystals were screened from the Fv-antibody library using MSU crystals as probes. Five CDR3 sequences were successfully screened as MSU-binding sequences from the Fv-antibody library, and these were synthesized into 11-residue peptides. Among these, two MSU-binding peptides (Nos. 1 and 3) showed a significantly higher affinity for preventing the growth of MSU crystals. A detection kit for MSU crystals was developed using MSU-binding peptide No. 3 (biotin-labeled). An assay was performed using samples from patients with gout (n = 23) and healthy controls (n = 29). The sensitivity and specificity of this assay were estimated to be 82.6

Perovskites are semiconductor materials with the ABX3 structure, and they possess several attractive features, such as a tunable bandgap, high photoluminescence quantum yield (PLQY), charge mobility, and carrier lifetime. Hence, they are widely used in various applications, such as light-emitting devices, solar cells, and photosensors. However, the perovskite defects, including grain boundaries, vacancies, ion migration, and structural deformation, interfere with the effective performance of the perovskite-based devices. The intrinsic instability and trap states caused by the perovskite defects decrease the stability and performance of perovskite-based devices. Two methods of defect passivation are carried out to enhance the effectiveness of perovskite-based devices: (1) polymers and (2) chemical additives. Defect passivation protects the surface to increase stability and reduce trap states, thereby enhancing the performance of perovskite-based devices. This article reviews the technologies for defect passivation in perovskite-based devices. The effect of defect passivation has been analyzed using various methodologies: (1) surface analysis using atomic force microscopy (AFM) and scanning electron microscopy (SEM), (2) bandgap and charge carrier lifetime analysis using photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra, (3) the trap-state density calculations based on the I–V curve under dark conditions, and (4) comparison of the critical parameters of the perovskite-based devices. This review provides an overview of the defect passivation technologies available to enhance the stability and applicability of perovskite-based photosensors.

In this work, we investigated the effect of hole transporting poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) interfacing with Mn-doped CdS/ZnS quantum dots (QDs) deposited on an indium tin oxide (ITO) substrate on the photoemission of upconverted hot electrons under weak continuous wave photoexcitation in a vacuum. Among the various factors that can influence the photoemission of the upconverted hot electrons, we studied the role of PEDOT:PSS in facilitating the hole transfer from QDs and altering the energy of photoemitted hot electrons. Compared to hot electrons emitted from QDs deposited directly on the ITO substrate, the addition of the PEDOT:PSS layer between the QD and ITO layers increased the energy of the photoemitted hot electrons. The increased energy of the photoemitted hot electrons is attributed in part to the reduced steady-state positive charge on the QDs under continuous photoexcitation, which reduces the energy required to eject the electron from the conduction band.

In this study, a homogeneous one-step immunoassay based on switching peptides is presented for the detection of influenza viruses A and B (Inf-A and Inf-B, respectively). The one-step immunoassay represents an immunoassay method that does not involve any washing steps, only treatment of the sample. In this method, fluorescence-labeled switching peptides quantitatively dissociate from the antigen-binding site of immunoglobulin G (IgG). In particular, the one-step immunoassay based on soluble detection antibodies with switching peptides is called a homogeneous one-step immunoassay. The immunoassay developed uses switching peptides labeled with two types of fluorescence dyes (FAM and TAMRA) and detection antibodies labeled with two types of fluorescence quenchers (TQ2 for FAM and TQ3 for TAMRA). The optimal switching peptides for the detection of Inf-A and Inf-B have been selected as L1-peptide and H2-peptide. The interactions between the four kinds of switching peptides and IgG have been analyzed using computational docking simulation and SPR biosensor. The location of labeling for the fluorescence quenchers has been determined based on the distance between the fluorescence dyes of the switching peptides and the fluorescence quenchers, calculated on the basis of the efficiency of fluorescence quenching, using the Förster equation. To demonstrate the feasibility of the one-step immunoassay, binding constants (KD) have been calculated for detection antibodies against Inf-A and Inf-B with target antigens (Inf-A and Inf-B) and switching peptides (L1- and H2-peptides), using an isotherm model. The immunoassay has been demonstrated to be feasible using antigens as well as real samples of Inf-A and Inf-B with a critical cycle number (Ct). The immunoassay has also been compared to other commercially available rapid test kits for Inf-A and Inf-B and found to be far more sensitive for detection of Inf-A and Inf-B over the entire detection range.

A one-step immunoassay is presented for the detection of ochratoxin A (OTA) using an antibody complex with switching peptides. Because the switching peptides (fluorescence-labeled) were able to bind the frame region of antibodies (IgGs), they were dissociated from antibodies immediately when target analytes were bound to the binding pockets of antibodies. From the fluorescence signal measurements of switching peptides, a quantitative analysis of target analytes, via a one-step immunoassay without any washing steps, could be performed. As the first step, the binding constant (KD) of OTA to the antibodies was estimated under the continuous flow conditions of a surface plasmon resonance biosensor. Then, the optimal switching peptide, among four types of switching peptides, and the reaction condition for complex formation with the switching peptide were determined for the one-step immunoassay for OTA analysis. Additionally, the selectivity test of one-step immunoassay for OTA was carried out in comparison with phenylalanine and zearalenone. For the application to the one-step immunoassay to detect OTA in wines, two types of sample pre-treatment methods were compared: (1) a liquid extraction was carried out using chloroform as a solvent with subsequent resuspension in phosphate-buffered saline (total analysis time < 1 h); (2) direct dilution of the wine sample (total analysis time < 0.5 h). Finally, the direct dilution method was found to be effective for the one-step immunoassay based on the switching peptide assay for OTA in wines with a markedly improved total analysis time (< 0.5 h). Additionally, the assay results were compared with commercial lateral flow immunoassay.

Parylene microfluidic systems have been utilized for applications requiring properties such as high chemical resistance, high internal pressure, high mechanical strength, and small heat loss. However, they have not been widely used compared to PDMS microfluidics because the device fabrication is relatively complex and surface functionalization is difficult. In this work, we introduce a simple and economic fabrication method for parylene microfluidic devices by molding and bonding using thin-film parylene A as an adhesive layer. The amine functional group from parylene A leverages as a covalent bonding source in between two parylene layers while providing the capability of functionalization of the internal surface of parylene microfluidic channel that is highly resistant to harsh chemicals at the same time. This new approach demonstrates the ability of high bonding strength (~ 4 Mpa) and eliminates the use of an additional adhesive polymer layer, which often fails to provide sufficient chemical resistance.

One-step immunoassay detects a target analyte simply by mixing a sample with a reagent solution without any washing steps. Herein, we present a one-step immunoassay that uses a peptide mimicking a target analyte (mimotope). The key idea of this strategy is that the mimotopes are screened from an autodisplayed FV-antibody library using monoclonal antibodies against target analytes. The monoclonal antibodies are bound to fluorescence-labeled mimotopes, which are quantitatively released into the solution when the target analytes are bound to the monoclonal antibodies. Thus, the target analyte is detected without any washing steps. For the mimotope screening, an FV-antibody library was exhibited on the outer membrane of E. coli with a diversity of >106 clones/library using autodisplay technology. The targeted clones were screened from the autodisplayed FV-antibody library using magnetic beads with immobilized monoclonal antibodies against food allergens. The analysis of binding properties of a control strain with mutant FV -antibodies composed of only CDR1 and CDR2 demonstrated that the CDR3 regions of the screened FV-antibodies showed binding affinity to food allergens. The CDR3 regions were synthesized into peptides as mimotopes for the corresponding food allergens (mackerel, peanuts, and pig fat). One-step immunoassays for food allergens were demonstrated using mimotopes against mackerel, peanut, and pig fat without any washing steps in solution without immobilization of antibodies to a solid support.

Nanostructures─coupled with mass spectrometry─have been intensively investigated to improve the detection sensitivity and reproducibility of small biomolecules in laser desorption/ionization mass spectrometry (LDI-MS). However, the impact of laser-induced shock wave on the ionization of the nanostructures has rarely been reported. Herein, we systematically elucidate the laser shock wave effect on the ionization in terms of the in situ development of atomic defects and piezoelectricity in two-dimensional graphitic carbon nitride nanosheets (g-C3N4 NS) by short laser pulses. The mass analysis results of immunosuppressive drugs verify the enhanced LDI-MS performance, structurally originating from anisotropic lattice distortions in g-C3N4 NS, i.e., in-plane extension (contraction) and out-of-plane contraction (extension) that modulate the charge carrier motion. Along with the experimental investigations, density functional theory calculations on Mulliken charges and dipole moments demonstrate the contribution of defect and piezoelectricity to the ionization. The results of this study provide a mechanistic understanding of the underlying ionization processes, which is crucial for revealing the full potential of laser shock waves in LDI-MS.

A one-step immunoassay based on filtration was presented, which used microbeads for target analyte detection and filters with appropriate pore sizes to distinguish the complexity of target analyte and microbeads. For effective bacterial detection, the microbead size and the filter's pore size must be optimized. The optimal con-centrations of the enzyme (urease) and antibody were determined at the maximum absorbance change, that is, the maximum pH change. The pH change was measured using a field-effect transistor (FET). The correlation between pH change and threshold voltage was estimated to be 21.7 mV/pH, and the correlation between pH change and the source-drain current was estimated to be-379 nA/pH. For the one-step immunoassay, antibodies against target bacteria were isolated from horse serum by filtration, and these antibodies were estimated to have a sufficiently high specificity to overcome cross-reactivity among five types of food poisoning-related bacteria: Escherichia coli O157, Salmonella typhimurium, Listeria monocytogenes, Bacillus cereus, and Staphylococcus aureus. Finally, the FET-based one-step immunoassay was demonstrated for five types of food poisoning-related bacteria in human serum.

Vertically paired electrodes (VPEs) with multiple electrode pairs were developed for the enhancement of capacitive measurements by optimizing the electrode gap and number of electrode pairs. The electrode was fabricated using a conductive polymer layer of PEDOT:PSS instead of Ag and Pt metal electrodes to increase the VPE fabrication yield because the PEDOT:PSS layer could be effectively etched using a reactive dry etching process. In this study, sensitivity enhancement was realized by decreasing the electrode gap and increasing the number of VPE electrode pairs. Such an increase in sensitivity according to the electrode gap and the number of electrode pairs was estimated using a model analyte for an immunoassay. Additionally, a computer simulation was performed using VPEs with different electrode gaps and numbers of VPE electrode pairs. Finally, VPEs with multiple electrode pairs were applied for SARS-CoV-2 nucleoprotein (NP) detection. The capacitive biosensor based on the VPE with immobilized anti-SARS-CoV-2 NP was applied for the specific detection of SARS-CoV-2 in viral cultures. Using viral cultures of SARS-CoV-2, SARS-CoV, MERS-CoV, and CoV-strain 229E, the limit of detection (LOD) was estimated to satisfy the cutoff value (dilution factor of 1/800) for the medical diagnosis of COVID-19, and the assay results from the capacitive biosensor were compared with commercial rapid kit based on a lateral flow immunoassay.

Several endemic corona viruses (eCoVs) have been reported to be the most common etiologic agents for the seasonal common cold and also cause pneumonia. These eCoVs share extensive sequence homology with SARS-CoV-2, and immune responses to eCoVs can cross-react with SARS-CoV-2 antigens. Based on such cross-reactivity of antigens among eCoVs, the IgG antibodies against the spike protein (SP) of severe acute respiratory syndrome coronavirus (SARS-CoV) were isolated from pig serum using magnetic beads immobilized with SARS-CoV SP and a protein-A column. The selectivity of the isolated antibodies was tested using different types of antigens, such as SARS-CoV-2 nucleoprotein (NP), influenza A virus (Beijing type), influenza B virus (Tokio and Florida types), human hepatitis B virus surface antigen (HBsAg), and bovine serum albumin (BSA). From the selectivity test, the anti-SP antibodies isolated from pig serum had sufficient selectivity to other kinds of viral antigens, and the apparent binding constant of the isolated antibodies was approximately 1.5 × 10–8 M from the surface plasmon resonance (SPR) measurements. Finally, the isolated anti-SP antibodies were applied to the immunoassay of SP using competitive immunoassay configuration. The feasibility of the detection as well as the quantitative analysis of the SARS-CoV viral culture fluid was determined using four viral culture samples, namely, SARS-CoV, SARS-CoV-2, MERS-CoV, and CoV-229E.

This study aimed to isolate FV-antibodies with biotin-binding activity from a FV-antibody library that was successfully screened on the outer membrane of E. coli. The aims were achieved by (1) preparing a library of FV-antibodies on the outer membrane of E. coli using autodisplay technology, (2) screening the FV-antibodies with biotin-binding activity from the FV-antibody library, and (3) synthesizing peptides (molecular weight of several kDa) from the biotin-binding amino acid sequence of FV-antibodies. An FV-antibody library with a diversity of 1.7 × 105 clones was prepared on the outer membrane of E. coli, using a surface display method called autodisplay technology. For the screening of biotin-binding FV-antibodies, the fluorescence-labeled biotin was introduced into the library, and the target E. coli with biotin-binding activity were screened using flow cytometry. For the screened E. coli clones, the binding affinity (KD) of Fv-antibodies against biotin was calculated and the binding properties of the screened FV-antibody were analyzed through competition assay with a synthetic peptide having the biotin-like activity. From the FRET experiment with the synthetic peptide corresponding to the CDR3 region of the screened Fv-antibody, the biotin-binding activity of the screened FV-antibody was proved to be originated from the CDR3. Finally, the applicability of the biotin-binding domain was demonstrated through the co-expression with a protein called Z-domain with antibody binding activity.

As the shelf life of platelets collected from donated blood is very short, approximately 5 days, the determination of bacterial contamination in platelets has become necessary. In this study, rapid analysis of Gram-positive and Gram-negative bacterial contamination in platelet samples was presented without pre-enrichment using pig serum-derived antibodies against the outer membrane proteins (OMP) of Gram-negative bacteria and antibodies against lipoteichoic acid (LTA) on the surface of Gram-positive bacteria. The anti-OMP antibodies against Gram-negative bacteria were isolated using sequential incubation with (1) the modified Gram-negative bacteria ClearColi, which lacks lipopolysaccharide (LPS) on the outer membrane, and (2) the Gram-positive bacteriaBacillus subtilis to filter away nonspecifically bound proteins from ClearColi. The anti-lipoteichoic acid (LTA) antibodies against Gram-positive bacteria were isolated using sequential incubation with (1) the Gram-positive bacteriaB. subtilis and (2) the Gram-negative bacteria Escherichia coli BL21 to filter away nonspecifically bound proteins fromB. subtilis. The feasibility of using the antibodies isolated from pig serum against Gram-negative and Gram-positive bacteria was demonstrated using flow cytometry. Finally, detection of the contamination of platelets with Gram-negative and Gram-positive bacteria using the impedance immunosensor based on these isolated antibodies was successfully demonstrated.

The physicochemical properties of nanostructured substrates significantly impact laser desorption/ionization mass spectrometry (LDI‐MS) performance. Fundamental understanding of the substrate properties can provide insights into the design and development of an efficient LDI matrix. Herein, a hybrid matrix of nanoporous Au‐modified TiO 2 nanowires (npAu‐TNW) is developed to achieve enhanced LDI‐MS performance. Its origin is investigated based on hybrid matrix properties including photo–thermal conversion and electronic band structure. Notably, further improvement is obtained in the npAu‐TNW than in the pristine TNW and non‐porous Au nanoisland‐modified TNW (Au‐TNW) hybrid, which is attributed to the laser‐induced surface restructuring/melting phenomenon. Noticeable surface restructuring/melting occurs in the npAu by laser exposure through efficient photo–thermal conversion of the highly porous npAu. At this instant of npAu structural changes, internal energy transfer from the npAu to the adsorbed analyte is promoted, which facilitates desorption. Moreover, strain is developed in situ in the TNW adjacent to the restructuring npAu, which distorts the TNW lattice. The strain development reduces recombination rates of charge carriers by introducing shallow trap levels in the bandgap, which enhances the ionization process. Ultimately, the high LDI‐MS performance based on the npAu‐TNW hybrid matrix is demonstrated by analyzing neurotransmitter.

A new method that uses plasma energy for the deposition of parylene-C films is presented. The equipment and instrumentation for the plasma deposition of parylene-C films were developed and constructed by combining evaporation and plasma-generating units. The plasma deposition of parylene-C films consists of three steps: evaporation, decomposition of the parylene-C dimers using plasma, and deposition of the film. The entire deposition process from evaporation to deposition was designed to be completed within 20 min for a parylene-C film with a thickness of less than 200 nm. The thickness of the parylene-C film was controlled in the range of 100-200 nm by adjusting the amount of parylene-C dimer as well as the plasma energy. The parylene-C films prepared by plasma deposition were characterized and compared with those obtained using the conventional pyrolysis method. The comparison included the chemical properties (chemical functional groups, atomic compositions) and their physical properties (density, crystallinity, absorption in the visible wavelength range, surface roughness and contact angle).

Herein, we present switching-peptides for a one-step immunoassay, without the need for additional antibody treatment or washing steps to detect antigen-antibody interactions. Fluorescently labeled switching-peptides were dissociated from the immobilized antibody soon after the antigens were bound to the binding pockets. In this study, four different parts of the antibody (IgG) frame regions were chemically synthesized, and these peptides were bound to immobilized antibodies as switching-peptides. We presented the design principle of switching-peptides and used Pymol software, based on the changes in thermodynamic parameters, to study the interaction between antibodies and switching-peptides. The binding properties of switching-peptides were analyzed based on Förster resonance energy transfer between switching-peptides as well as between switching-peptides and antibodies (IgGs) isolated from different animals. The binding constants of the four switching-peptides to antibodies were estimated to be in the range of 1.48-3.29 μM. Finally, the feasibility of using switching-peptides for the quantitative one-step immunoassay was demonstrated by human hepatitis B surface antigen (hHBsAg) detection and statistical comparison of the assay results with those of conventional ELISA. The limit of detection for HBsAg was determined to be 56 ng/mL, and the dynamic range was estimated to be 136 ng/mL-33 μg/mL. These results demonstrate the feasibility of the one-step immunoassay for HBsAg.

Anti-severe acute respiratory syndrome coronavirus 2 (anti-SARS-CoV-2) nucleoprotein (NP) antibodies were isolated from pig sera using human SARS-CoV-2 NP-immobilized magnetic beads. The binding properties of the isolated antibodies against SARS-CoV-2 NP were tested via flow cytometry using SARS-CoV-2 NP-immobilized magnetic beads. A competitive immunoassay was developed for detecting SARS-CoV-2 NP as well as SARS-CoV-2 in the culture fluid using magnetic beads with immobilized anti-SARS-CoV-2 NP antibodies. Selectivity tests were carried out during the competitive immunoassay for SARS-CoV, MERS-CoV, and CoV strain 229E in the culture fluid.

Many conventional optical biosensing systems use a single responsive signal in the visible light region. This limits their practical applications, as the signal can be readily perturbed by various external environmental factors. Herein, a near-infrared (NIR)-based self-calibrating luminescence resonance energy transfer (LRET) system was developed for background-free detection of analytes in homogeneous sandwich-immunoassays. The inorganic LRET pair was comprised of NIR dual-emitting lanthanide-doped nanoparticles (LnNPs) as donors and NIRabsorbing LnNPs as acceptors, which showed a narrow absorption peak (800 nm) and long-term stability, enabling stable LRET with a built-in self-calibrating signal. Screened single-chain variable fragments (scFvs) were used as target avian influenza virus (AIV)-binding antibodies to increase the LRET efficiency in sandwich immunoassays. The compact sensor platform successfully detected AIV nucleoproteins with a 0.38 pM limit of detection in buffer solution and 64 clinical samples. Hence, inorganic LnNP pairs may be effective for self calibrating LRET systems in the background-free NIR region.

Cadmium sulfide (CdS) is an II–VI semiconductor with a direct bandgap of 2.4 eV; it has been used for various applications, such as nonlinear optical devices, flat-panel displays, light-emitting diodes, lasers, logic gates, transistors, photoresistors, solar cells, infrared waveguides, and splitters. CdS nanostructures have been synthesized through two different routes: (1) vapor-phase growth and (2) liquid-phase growth. The vapor-phase growth system can yield highly pure single-crystal nanostructures, and liquid-phase growth has been carried out through chemical or electrochemical reactions in solution with templates. The fabricated nanostructures of CdS showed a relatively low work function, high refractive index, excellent transport properties, good chemical capability, thermal stability, high electronic mobility, and piezoelectric properties. For these reasons, CdS photosensors have been produced using various nanostructures of CdS, such as nanorods, nanoribbons, and nanowires. For the fabrication of CdS nanowire photosensors, many different approaches have been demonstrated to connect nanostructures in devices and circuits using various techniques, such as dry transfer, wet transfer, and contact printing. Each method has practical advantages and drawbacks in the implementation of nanostructures in devices. In this article, the synthesis of CdS nanostructures and the fabrication of photosensors based on the CdS nanostructures are reviewed.

A novel method for quantifying galactose was developed to serve as a newborn screening test for galactosemia using laser desorption/ionization time-of-flight (LDI-TOF) mass spectrometry (MS) with a TiO2 nanowire chip. Herein, phosphate citrate buffer, serum, and dried blood spot (DBS) were employed for the quantitative analysis of galactose. To quantitatively analyze galactose, its reduction potential was used to oxidize o-phenylene diamine (OPD) into 2,3-diaminophenazine (DA), which were both detected using LDI-TOF MS with a TiO2 nanowire chip according to the concentration of galactose. The reproducibility and the interference of glucose were determined to demonstrate the applicability of this method. Moreover, mixtures of galactose, phenylalanine, and 17 α-OHP were analyzed to determine the interference induced by other biomarkers of metabolic disorders. The OPD oxidation of galactose was found to be selectively achieved under high-glucose conditions, similar to human blood, thereby showing good reproducibility. The intensities of the mass peaks of OPD and DA based on LDI-TOF MS with a TiO2 nanowire chip were linearly correlated in the galactose concentration range of 57.2–220.0 μg/mL (r2 = 0.999 and 0.950, respectively) for serum samples and 52.5–220.0 μg/mL (r2 = 0.993 and 0.985, respectively) for DBS after methanol precipitation/extraction. The enzyme immunoassay and LDI-TOF MS analysis results were statistically analyzed, and a mixture of phenylalanine, 17 α-OHP, and galactose was simultaneously investigated quantitatively at the cutoff level.