A multiple signal amplification photoelectrochemical biosensor based on biotin-avidin system for kanamycin sensing in fish and milk via synergism of g-C3N4 and Ru@SiO2

BACKGROUND

The residues of kanamycin can accumulate in the human body for a long time and pose serious health risks, including hearing loss, kidney poisoning, and drug allergic reactions. Therefore, it is crucial to develop a rapid, highly sensitive, and low-cost method for detecting kanamycin residues in foods. However, the current methods have limitations such as low sensitivity, expensive instruments, and multiple steps, which make them impractical for use in resource-limited environments and emergencies. In this study, the creation of a multiple-signal amplification photoelectrochemical biosensor to address these aforementioned issues is discussed.

RESULTS

Herein, we proposed a multiple signal amplification photoelectrochemical (PEC) biosensor based on carboxylated g-C3N4 and avidin functionalized Ru@SiO2 for the ultrasensitive detection of kanamycin. The carboxylated g-C3N4 was a highly efficient photoactive substance for amplifying photoelectric signals and a substrate for aptamer immobilization. The DOS and PDOS of g-C3N4 were studied by simulation, and the sensing mechanism of the probe at the molecular level was revealed. Meanwhile, using Ru@SiO2 as a signal amplifying unit, through the cooperative work between Ru@SiO2 and g-C3N4, the photoelectric signal could be double amplified to produce an excellent photocurrent response. Under optimized conditions, the photocurrent response of the PEC biosensor to kanamycin was obtained at concentrations from 0.1 nM to 1000 nM with a lower detection limit of 4.1052 × 10-11 mol L-1. This protocol demonstrates high sensitivity, brilliant specific recognition ability, excellent reproducibility, and acceptable stability.

SIGNIFICANCE

The first combination of g-C3N4 and avidin-Ru@SiO2 as photocurrent materials greatly enhanced the sensitivity of the PEC biosensors. Moreover, the specificity and sensitivity of the PEC biosensor were further improved through the specific interaction between kanamycin and aptamer. The photoelectric conversion mechanism based on g-C3N4 and two pathways for enhancing the photocurrent by Ru(byp)32+ were proposed. Through simulations of the DOS and PDOS of g-C3N4, the sensing mechanism of the probe at the molecular level was revealed. Under the optimum conditions, the PEC biosensor exhibited a wide linear concentration range and a low detection limit.

A Rapid and Simplified Method to Isolate Specific Regulators Based on Biotin-Avidin Binding Affinities in Crops

Transcription factors (TFs) are indispensable components of transcriptional regulatory pathways involved in crop growth and development. Herein, we developed a new method for the identification of upstream TFs specific to genes in crops based on the binding affinities of biotin and avidin. First, we constructed and verified the new biotin and avidin system (BAS) by a coprecipitation assay. Subsequently, the feasibility of DNA-based BAS (DBAS) was further proved by in vivo and in vitro assays. Furthermore, we cloned the promoter of rice OsNRT1.1B and the possible regulators were screened and identified. Additionally, partial candidates were validated by the electrophoresis mobility shift assay (EMSA), yeast one-hybrid, and luciferase activity assays. Remarkably, the results showed that the candidates PIP3 and PIP19 both responded to nitrate immediately and overexpression of PIP3 caused retard growth, which indicates that the candidates are functional and the new DBAS method is useful to isolate regulators in crops.

Development of an ultrasensitive sandwich immunoassay for detecting small molecule semicarbazide

Ultrasensitive sandwich immunoassays for detecting the small molecule semicarbazide (SEM) were developed based on derivatization. Several SEM derivatizing agents were synthesized by linking o-nitrobenzaldehyde (NBA) and biotin with dihydroxyalkanes (different lengths), which were then used to evaluate the distance effect of two epitopes. Sandwich ELISA for SEM derivatives was developed using an anti-SEM-NBA antibody and horseradish peroxidase-labeled avidin or anti-biotin antibody as a secondary conjugate. The advantageous distances of the two epitopes under the double-antibody sandwich and antibody-avidin sandwich modes were ≥12 and ≥13 Å, respectively. Under the distances, the sensitivities of the sandwich ELISA were no lower than those of competitive ELISA. The obtained optimal EC50 values were 11.2 pg/mL (double-antibody sandwich with the epitope distance ≥16 Å) and 7.3 pg/mL (antibody-avidin sandwich with the epitope distance ≥17 Å). Compared with competitive ELISA, the developed method achieved a 30-fold improvement in sensitivity, with simpler aquatic product pretreatment.

Biotinylated Quinone as a Chemiluminescence Sensor for Biotin-Avidin Interaction and Biotin Detection Application

Biotin, or vitamin B7, is essential for metabolic reactions. It must be obtained from external sources such as food and biotin/vitamin supplements because it is not biosynthesized by mammals. Therefore, there is a need to monitor its levels in supplements. However, biotin detection methods, which include chromatographic, immune, enzymatic, and microbial assays, are tedious, time-consuming, and expensive. Thus, we synthesized a product called biotin-naphthoquinone, which produces chemiluminescence upon its redox cycle reaction with dithiothreitol and luminol; then it was used as a chemiluminescence sensor for biotin-avidin interaction. When a quinone biotinylated compound binds avidin, the chemiluminescence decreases noticeably due to the proximity between quinone and avidin, and when free biotin is added in a competitive assay, the chemiluminescence returns. The chemiluminescence is regained as the free biotin displaces biotinylated quinone in its complex with avidin, freeing biotin-naphthoquinone. Many experiments, including the use of a biotin-free quinone, proved the competitive nature of the assay. The competitive assay method used in this study was linear in the range of 1.0-100 µM with a detection limit of 0.58 µM. The competitive chemiluminescence assay could detect biotin in vitamin B7 tablets with good recovery of 91.3 to 110% and respectable precision (RSD < 8.7%).

Inhibiting Multidrug Resistance with Transferrin-Targeted Polymersomes through Optimization of Ligand Density

Transferrin-conjugated polymersomes, transferrin-biotin/avidin/biotin-Pluronic F127-poly(lactic acid) (Tf-F127-PLA), were successfully prepared through a biotin-avidin bridging technique to study their ability to inhibit multidrug resistance of cancer cells. Hydrophilic doxorubicin (DOX) was selected as the model drug to be loaded into Tf-F127-PLA polymersomes. DOX loaded in Tf-F127-PLA polymersomes was released fast initially, followed by a slow release. The effect of the transferrin ligand density of Tf-F127-PLA/DOX polymersomes on their targeting properties was studied by both cytotoxicity and cellular uptake assays against A549 lung cancer cells. It was shown that Tf-F127-PLA/DOX polymersomes had better targeting ability than nontargeted drug-loaded polymersomes. Furthermore, Tf-F127-PLA/DOX polymersomes with 2% Tf molar content have more effective antitumor activity and a higher cellular uptake than those with 4 and 5% Tf molar content. 2% Tf-F127-PLA/DOX polymersomes also exhibited better anticancer ability in multidrug resistant cancer cells A549/ADR than nontargeted PLA-F127-PLA/DOX polymersomes. It was further proved that the endocytosis of polymersomes by A549/ADR cells was an energy-dependent endocytosis process, which was related to clathrin, macrocytosis, and caveolin. Also, the endocytosis of Tf-F127-PLA/DOX polymersomes was proven to be mediated by the transferrin receptor.

A picogram BA-ELISA quantification assay for rLj-RGD3, a platelet fibrinogen receptor antagonist, in the rat plasma and its application to a pharmacokinetic study

rLj-RGD3, a new member of the RGD (Arginine-Glycine-Aspartate)-motif toxin protein family obtained from Lampetra japonica by means of recombinant DNA techniques, has been demonstrated to be a platelet fibrinogen receptor antagonist and holds potential as a drug candidate for a specific indication. The present article reports an innovative validated highly sensitive and specific biotin-avidin enzyme linked immunosorbent assay (BA-ELISA) to provide a bio-analytical method for pharmacokinetic (PK) studies of rLj-RGD3. The concentration of picogram level rLj-RGD3 in rat plasma was measured using the developed double sandwich BA-ELISA assay, which used two mouse anti-rLj-RGD3 monoclonal antibodies that recognize different epitopes for capture and detection. This method was verified to be highly specific (blank plasma did not interfere with detection), precise (RSD <15%), and accurate (86%-113%). Absolute recovery was in the 94%-119% range. The calibration curve showed good linearity within the 50 to 1600 pg/mL range. The LOQ was as low as 50 pg/mL. The above validated assay was successfully employed to assess PK of rLj-RGD3 in rats. After i.v. and s.c. dosing with 30 μg/kg, the rLj-RGD3 plasma concentration declined bi-exponentially with time. This decay was best fitted to a two-compartment model. In conclusion, the BA-ELISA method described here meets all requirements for PK studies of rLj-RGD3 with an effective pharmacological dose in the μg/kg BW range.

Immunostaining-Based Detection of Dynamic Alterations in Red Blood Cell Proteins

Antibody labeling of red blood cell (RBC) proteins is a commonly used, semi-quantitative method to detect changes in overall protein content or acute alterations in protein activation states. It facilitates the assessment of RBC treatments, characterization of differences in certain disease states, and description of cellular coherencies. The detection of acutely altered protein activation (e.g., through mechanotransduction) requires adequate sample preparation to preserve otherwise temporary protein modifications. The basic principle includes immobilizing the target binding sites of the desired RBC proteins to enable the initial binding of specific primary antibodies. The sample is further processed to guarantee optimal conditions for the binding of the secondary antibody to the corresponding primary antibody. The selection of non-fluorescent secondary antibodies requires additional treatment, including biotin-avidin coupling and the application of 3,3-diaminobenzidine-tetrahydrochloride (DAB) to develop the staining, which needs to be controlled in real-time under a microscope in order to stop the oxidation, and thus staining intensity, on time. For staining intensity detection, images are taken using a standard light microscope. In a modification of this protocol, a fluorescein-conjugated secondary antibody can be applied instead, which has the advantage that no further development step is necessary. This procedure, however, requires a fluorescence objective attached to a microscope for staining detection. Given the semi-quantitative nature of these methods, it is imperative to provide several control stains to account for non-specific antibody reactions and background signals. Here, we present both staining protocols and the corresponding analytical processes to compare and discuss the respective results and advantages of the different staining techniques.

Reduced Graphene Oxide-Polydopamine-Gold Nanoparticles: A Ternary Nanocomposite-Based Electrochemical Genosensor for Rapid and Early Mycobacterium tuberculosis Detection

Tuberculosis (TB) has been a devastating human illness for thousands of years. According to the WHO, around 10.4 million new cases of tuberculosis are identified every year, with 1.8 million deaths. To reduce these statistics and the mortality rate, an early and accurate TB diagnosis is essential. This study offers a highly sensitive and selective electrochemical biosensor for Mycobacterium tuberculosis (MTB) detection based on a ternary nanocomposite of reduced graphene oxide, polydopamine, and gold nanoparticles (rGO-PDA-AuNP). Avidin-biotin coupling was used to bind the MTB probe DNA onto the rGO-PDA-AuNP modified glassy carbon electrode (ssDNA/avidin/rGO-PDA-AuNP). UV-Visible, Raman, XRD, and TEM were used to evaluate the structural and morphological characteristics of rGO-PDA-AuNP. Furthermore, DNA immobilization is validated using FESEM and FT-IR techniques. The modified electrodes were electrochemically analyzed using cyclic voltammetry (CV) and linear sweep voltammetry (LSV), and the results indicate that the produced electrode can detect target DNA up to 0.1 × 10^-7 mM with 2.12 × 10^-3 mA µM^-1 sensitivity and a response time of 5 s. The constructed genosensor displayed high sensitivity and stability, and it also provides a unique strategy for diagnosing MTB at an early stage. Furthermore, our rGO-PDA-AuNP/GCE-based electrochemical platform has broad potential for creating biosensor systems for detecting various infectious pathogens and therapeutically significant biomarkers.

Intraprocedural endothelial cell seeding of arterial stents via biotin/avidin targeting mitigates in-stent restenosis

Impaired endothelialization of endovascular stents has been established as a major cause of in-stent restenosis and late stent thrombosis. Attempts to enhance endothelialization of inner stent surfaces by pre-seeding the stents with endothelial cells in vitro prior to implantation are compromised by cell destruction during high-pressure stent deployment. Herein, we report on the novel stent endothelialization strategy of post-deployment seeding of biotin-modified endothelial cells to avidin-functionalized stents. Acquisition of an avidin monolayer on the stent surface was achieved by consecutive treatments of bare metal stents (BMS) with polyallylamine bisphosphonate, an amine-reactive biotinylation reagent and avidin. Biotin-modified endothelial cells retain growth characteristics of normal endothelium and can express reporter transgenes. Under physiological shear conditions, a 50-fold higher number of recirculating biotinylated cells attached to the avidin-modified metal surfaces compared to bare metal counterparts. Delivery of biotinylated endothelial cells to the carotid arterial segment containing the implanted avidin-modified stent in rats results in immediate cell binding to the stent struts and is associated with a 30% reduction of in-stent restenosis in comparison with BMS.

A microfluidics-based method for isolation and visualization of cells based on receptor-ligand interactions

Receptor-ligand binding has been analyzed at the protein level using isothermal titration calorimetry and surface plasmon resonance and at the cellular level using interaction-associated downstream gene induction/suppression. However, no currently available technique can characterize this interaction directly through visualization. In addition, all available assays require a large pool of cells; no assay capable of analyzing receptor-ligand interactions at the single-cell level is publicly available. Here, we describe a new microfluidic chip-based technique for analyzing and visualizing these interactions at the single-cell level. First, a protein is immobilized on a glass slide and a low-flow-rate pump is used to isolate cells that express receptors that bind to the immobilized ligand. Specifically, we demonstrate the efficacy of this technique by immobilizing biotin-conjugated FGL2 on an avidin-coated slide chip and passing a mixture of GFP-labeled wild-type T cells and RFP-labeled FcγRIIB-knockout T cells through the chip. Using automated scanning and counting, we found a large number of GFP+ T cells with binding activity but significantly fewer RFP+ FcγRIIB-knockout T cells. We further isolated T cells expressing a membrane-anchored, tumor-targeted IL-12 based on the receptor's affinity to vimentin to confirm the versatility of our technique. This protocol allows researchers to isolate receptor-expressing cells in about 4 hours for further downstream processing.

Protein-structure-dependent spectral shifts of near-infrared photoluminescence from locally functionalized single-walled carbon nanotubes based on avidin-biotin interactions

Single-walled carbon nanotubes (SWCNTs) emit photoluminescence (PL) in the near-infrared (NIR) region (>900 nm). To enhance their PL properties, defect doping via local chemical functionalization has been developed. The locally functionalized SWCNTs (lf-SWCNTs) emit red-shifted and bright E₁₁* PL originating from the excitons localized at the defect-doped sites. Here, we observe the E₁₁* PL energy shifts induced by protein adsorption via the avidin-biotin interactions at the doped sites of lf-SWCNTs. We establish that the difference in the structures of the avidin derivatives notably influences the energy shifts. First, lf-SWCNT-tethering biotin groups (lf-SWCNTs-b) are synthesized based on diazonium chemistry, followed by post-modification. The responsiveness of the lf-SWCNTs-b to different microenvironments is investigated, and a correlation between the E₁₁* PL energy shift and the induction-polarity parameters of surrounding solvents is established. The adsorption of neutravidin onto the lf-SWCNTs-b induces an increase in the induction-polarity parameters around the biotin-doped sites, resulting in the red-shift of the E₁₁* PL peak. The E₁₁* PL shift behaviors of the lf-SWCNTs-b change noticeably when avidin and streptavidin are introduced compared to the case with neutravidin. This is due to the different microenvironments formed at the biotin-doped sites, attributed to the difference in the structural features of the introduced avidin derivatives. Moreover, we successfully enhance the detection signals of lf-SWCNTs-b (>three fold) for streptavidin detection using a fabricated film device. Therefore, lf-SWCNTs exhibit significant promise for application in advanced protein detection/recognition devices based on NIR PL.

In vivo Detection of Macromolecule Free Radicals in Mouse Sepsis-Associated Encephalopathy Using a New MRI and Immunospin Trapping Strategy

Introduction

Free radicals in oxidative stress are known to play a pathogenic role in sepsis. A major clinical challenge associated with sepsis is sepsis-associated encephalopathy (SAE). The rapid increase of free radicals in the brain promotes SAE progression. Here, macromolecule free radicals in the mouse brain were uniquely detected by immunospin trapping (IST) and magnetic resonance imaging (MRI).

Methods

The new strategy uses spin trapping agent DEPMPO-biotin to capture macromolecule free radicals in lesions and form biotin-DEPMPO-radical adducts. Then, a targeting MRI probe, avidin-BSA@Gd-ESIO, was used to detect the radical adducts through the highly specific binding of avidin and biotin. The avidin-BSA@Gd-ESIO probe was synthesized and systematically characterized. The detection capability of the new strategy was evaluated in vitro and in vivo using a confocal microscope and a 7T MRI, respectively.

Results

In reactive oxygen species (ROS)–induced microglial cells, the accumulation of the avidin-BSA@Gd-ESIO probe in the DEPMPO-biotin-treated group was significantly higher than that of control groups. In vivo MRI T1 signal intensities were significantly higher within the hippocampus, striatum, and medial cortex of the brain in mice with a mild or severe degree of sepsis compared with the sham control group. Histological analysis validated that the distribution of the avidin-BSA@Gd-ESIO probe in brain tissue slices was consistent with the MRI images. The fluorescence signals of ROS and avidin-BSA@Gd-ESIO probe were overlapped and visualized using immunofluorescent staining. By evaluating the T1 signal changes over time in different areas of the brain, we estimated the optimal MRI detection time to be 30 minutes after the probe administration.

Discussion

This method can be applied specifically to assess the level of macromolecular free radicals in vivo in a simple and stable manner, providing a pathway for a more comprehensive understanding of the role of free radicals in SAE.

Antigen Retrieval and Signal Amplification

Immunohistochemistry (IHC) offers a valuable method for determining the spatial distribution of proteins in cells and tissues. Fixation of tissues prior IHC enables their long-term stability and preserves tissue morphology; however, downstream analysis of protein localization within fixed samples can be complicated by cross-links formed between proteins during formalin fixation which mask target epitopes. Antigen Retrieval (AR) is a process introduced to reverse such cross-links, improving the sensitivity of antibody-based protein detection, and can be performed using protease- or heat-based approaches. Even following AR, low abundance target proteins may require additional amplification for sensitive visualization. The development of amplification approaches such as the use of biotinylated secondary antibodies with avidin-biotin complex and tyramide signal amplification greatly improve the sensitivity of IHC, enabling a wider range of epitopes to be detected when coupled with AR.

Cationic Contrast Agents for Computed Tomography of Cartilage for Early Diagnosis of Osteoarthritis

Here we describe methods for synthesizing cationic contrast agents for computed tomography (CT) of cartilage for early diagnosis of tissue degeneration. CT imaging of soft tissues like cartilage is possible only if radio-opaque contrast agents (e.g., ioxaglate) can penetrate through the full thickness of tissue in sufficient concentrations. Ioxaglate (IOX), however, is anionic and is repelled by the negatively charged cartilage matrix resulting in poor CT attenuation. Here we demonstrate cartilage penetrating cationic contrast agents using multi-arm Avidin (mAv) conjugated to ioxaglate (mAv-IOX). mAv-IOX rapidly penetrates through the full thickness of cartilage in high concentrations owing to weak-reversible nature of electrostatic interactions resulting in high CT attenuation even with low doses unlike IOX. The technology has the potential for enabling clinical CT of cartilage and other negatively charged soft tissues.

Detection of Lung Cancer Cells in Solutions Using a Terahertz Chemical Microscope

Cancer genome analysis has recently attracted attention for personalized cancer treatment. In this treatment, evaluation of the ratio of cancer cells in a specimen tissue is essential for the precise analysis of the genome. Conventionally, the evaluation takes at least two days and depends on the skill of the pathologist. In our group, a terahertz chemical microscope (TCM) was developed to easily and quickly measure the number of cancer cells in a solution. In this study, an antibody was immobilized on a sensing plate using an avidin-biotin reaction to immobilize it for high density and to improve antibody alignment. In addition, as the detected terahertz signals vary depending on the sensitivity of the sensing plate, the sensitivity was evaluated using pH measurement. The result of the cancer cell detection was corrected using the result of pH measurement. These results indicate that a TCM is expected to be an excellent candidate for liquid biopsies in cancer diagnosis.

Highly sensitive and rapid detection of porcine circovirus 2 by avidin-biotin complex based lateral flow assay coupled to isothermal amplification

In this study, a new platform for the detection of porcine circovirus 2 was developed by avidin-biotin complex based lateral flow assay (LAMP-LFA). Improved detection sensitivity was attained by using loop mediated isothermal amplification (LAMP) with a low limit of detection (LOD), so the platform can be used to detect even early or asymptomatic stages of infection. LFA, which requires no specialized equipment, facilitates the use of point-of-care (POC) tests. Therefore, by applying LFA, the result can be confirmed accurately with the naked eye. Moreover, this platform has a unique structure using a single-tag detection system. The avidin-biotin interaction is the strongest interaction between proteins and has a higher K_d value than antigen-antibody interactions. Thus, the results are stable and can be clearly confirmed. The high sensitivity of LAMP-LFA enables all steps to be completed in 30 min. As a result, it could be applied to different targets, such as other pathogens. Future POC diagnostic studies are expected to be of great practical benefit.

Immunosorbent assay based on upconversion nanoparticles controllable assembly for simultaneous detection of three antibiotics

The abuse of antibiotics leads to an increase in resistant strains, which in turn leads to the development of superbugs that pose great difficulties for the treatment of human diseases. A high-throughput and highly sensitive avidin biotin complex immunosorbent assay based on upconversion nanoparticles controllable assembly (ABC-ULISA) for the detection of antibiotics was developed, which enabled accurate quantitative detection in a shorter period of time. Streptavidin and biotin-labeled upconversion nanoparticles form avidin-biotin-upconversion complex, which was then combined with biotinylated antibody to achieve double amplification of the signal, further improving detection sensitivity. Upconversion nanoparticles with 808 nm excitation provide better penetration without the need for an external source. The 96-well enzyme-linked plate was used as a detection platform to meet the high-throughput needs. ABC-ULISA was used to simultaneously detect three antibiotics with a limit of detection of 0.15 ng/mL for sulfamethazine, 0.03 ng/mL for sarafloxacin, and 0.05 ng/mL for tetracycline. The detection limit of ABC-ULISA was much lower than the traditional ELISA and ordinary ULISA. Moreover, ABC-ULISA was also versatile, and the corresponding target can be detected by changing different antibodies. The results were stable and reliable, and the equipment could be miniaturized, which was expected to be commercialized and on-site.

Neutral DNA-avidin nanoparticles as ultrasensitive reporters in immuno-PCR

We have developed an immuno-PCR based diagnostic platform which couples detection antibodies to self-assembled, ultra-detectable DNA-avidin nanoparticles stabilized with poly(ethylene glycol) to link DNA amplification to target protein concentration. Electrostatic neutralization and cloaking of the PCR-amplifiable DNA labels by avidin and PEG coating reduces non-specific "stickiness" and enhances assay sensitivity. We further optimized the detectability of the nanoparticles by incorporating four repeats of a unique synthetic DNA PCR target into each nanoparticle. Using human chorionic gonadotropin hormone (hCG) as a model analyte, this platform was able to quantitate the target hCG protein in femtomolar concentrations using only standard laboratory equipment.

Size-adaptable and ligand (biotin)-sheddable nanocarriers equipped with avidin scavenging technology for deep tumor penetration and reduced toxicity

The conventional active-targeting nano-chemotherapy suffers from poor tumor tissue penetration and non-negligible toxicity due to the size/ligand dilemmas and insufficient target selectivity. In this report, a stimuli-responsive size-adaptable and ligand (biotin)-sheddable drug delivery system (DDS) combined with two-step strategy of biotin-avidin system was designed to seek a balance between tumor targeting and penetration as well as to self-scavenge the nonresponsive nanocarriers in normal tissues. This DDS was composed of 'multi-seed' polymeric liposomes (ASL-BIO-MPL) with asulacrine-loaded micelles as seeds in their aqueous cavities. The shell of such liposomes was modified with MMP-9 cleavable polymer-polypeptide functionalized with the tumor targeting ligand biotin. ASL-BIO-MPL could disintegrate into mixture of irregularly-shaped liposomes (~200 nm) and scattered tiny micelles (~40 nm) after incubation with MMP-9. The fluorescence-labeled BIO-MPL could travel to the center of the 4T1 breast tumor spheroids under the action of MMP-9, possibly benefited from the relay of released tiny micelles. Conversely, neither the biotin-modified micelles nor non-MMP-9-responsive multi-seed liposomes could penetrate into the spheroids possibly due to the potent binding-site barrier of biotin and large size, respectively. In tumor-bearing mice, ASL-BIO-MPL exhibited the strongest drug penetrability and thus the optimal inhibition of tumor growth compared to other formulations. Following administration of avidin with a rational dosage regimen, the number of apoptotic cells in normal tissues induced by ASL-BIO-MPL reduced without affecting their targeting effect, suggesting the followed administration of adivin could scavenge the DDS in non-target site. Overall, the size/ligand adapting MPL system combined with two-step strategy of biotin-avidin may provide potential avenues for nanocarriers to enhance deep tumor tissue targeting and protect normal tissues.

A Novel Diagnostic System for Infectious Diseases Using Solid-State Nanopore Devices

Nanopore-based diagnostic systems are a promising tool for counting viruses in a specimen one by one. However, despite intensive R&D efforts, it remains difficult to recognize virus subtypes by nanopore devices. We thus propose a novel diagnostic system that combines a specialized virus recognition procedure with a nanopore detection procedure. This recognition procedure consists of three steps: 1) capture target viruses using specific probes for recognition; 2) release captured targets; and 3) detect released targets by nanopore. Proof-of-concept tests are conducted using avidin-modified fluorescent particles (as a model for viruses) and biotin-modified alkane thiol (as a model for probes). The avidin-modified particles are confirmed to be captured on electrode by biotin-modified probes and then, the particles are electrochemically released from the electrode. Consequently, the released particles are successfully detected by nanopore devices. Furthermore, the concept is also proved by using human influenza viruses (H1N1, A/PR/8/34) and sugar chain (6'-sialyllactose)-modified probes. This suggests that our concept is applicable to various infectious diseases by changing probes (ligands).

Pretargeting of Carcinomas with the Avidin-Biotin System

Diagnosis and experimental therapy of cancer have been performed with encouraging results using radiolabelled monoclonal antibodies. However, the high background due to non-specific uptake by normal tissue and blood is a major drawback in antibody-guided tumor detection. Various strategies have been proposed to overcome this problem, such as computed background subtraction, use of a second antibody, and local delivery. An antibody is a slow “bullet” for tumor targeting, since in many lesions it requires two or three days to accumulate. The use of fragments such as F(ab’)2 or Fab, which display a faster blood clearance than whole antibody, improves tumor localization to a sufficient extent (hours) to allow the use of the most suitable radionuclides, e.g. 99m-Tc. In therapeutic applications we are still far away from the optimal condition in terms of the absolute amount of radioactivity delivered to the tumor. The high specificity of antibodies could be exploited at its best by delaying the delivery of the label to a time when the ratio tumor-bound to non-tumor-bound antibody has reached its maximum value. To obtain this goal, the label should display a fast clearance and should be captured by the antibody already targeted onto tumor cells. These considerations have led to strategies of tumor pretargeting where antibody and label are administered separately. One of these strategies, based on the avidin-biotin system, has already been used extensively for several years in immunohistochemistry and in ELISA. Due to the flexibility of this system, several alternative protocols are possible.

We describe a three-step and a two-step pretargeting protocol based on the avidin-biotin system.

Spatial and Chemical Surface Guidance of NK Cell Cytotoxic Activity

Studying how different signaling pathways spatially integrate in cells requires selective manipulation and control of different transmembrane ligand-receptor pairs at the same time. This work explores a novel method for precisely arranging two arbitrarily chosen ligands on a micron-scale two-dimensional pattern. The approach is based on lithographic patterning of Au and TiO₂ films, followed by their selective functionalization with Ni-nitrilotriacetic acid-histidine and biotin-avidin chemistries, respectively. The selectivity of chemical and biological functionalizations is demonstrated by X-ray photoelectron spectroscopy and immunofluorescence imaging, respectively. This approach is applied to produce the first type of bifunctional surfaces with controllably positioned ligands for activating the receptors of natural killer (NK) immune cells. NK cells were used as a model system to demonstrate the potency of the surface in guiding site-selective cell attachment and activation. Upon applying the suitable ligand or ligand combination, the surfaces guided the appropriate single- or bifunctional attachment and activation. These encouraging results demonstrate the effectiveness of the system as an experimental platform aimed at the comprehensive understanding of the immunological synapse. The great simplicity, modularity, and specificity of this approach make it applicable for a myriad of combinations of other biomolecules and applications, turning it into the "Swiss knife" of biointerfaces.

One-step fabrication of LSPR-tuneable reconfigurable assemblies of gold nanoparticles decorated with biotin-binding proteins

Assemblies of gold nanoparticles with chain-like morphologies and new near-infrared (NIR) localized surface plasmon resonance (LSPR) are obtained by adding the biotin-binding proteins avidin, neutravidin or streptavidin to citrate-capped nanoparticles. The key idea behind this one-step fabrication method is to destabilize the colloids by adding positively charged proteins and/or by making their zeta potential less negative. The extent of assembly, and therefore the NIR LSPR, can be fine-tuned by varying the concentration of proteins as well as by changing the pH of the solution. The resulting nanoparticle clusters can also reconfigure into smaller assemblies that absorb less NIR light by adding thiolated molecules or by increasing the pH of the solution. This, along with the observation that the proteins retain their biotin-binding properties in the assemblies, makes the proposed method promising for the development of new biosensors and drug delivery platforms capable of self-regulating their optical properties as a function of chemical signals in their environment.

Increasing Binding Efficiency via Reporter Shape and Flux in a Viral Nanoparticle Lateral-Flow Assay

To identify factors controlling the performance of reporter particles in a sensitive lateral-flow assay (LFA), we investigated the effect of the flux and shape of filamentous bacteriophage (phage) on the performance of phage LFAs. Phage of three different lengths and diameters were modified with biotin and AlexaFluor 555 as binding and read-out elements, respectively. The binding efficiencies of the functionalized phage were tested in a fibrous glass LFA membrane modified with avidin. The total binding rate, quantified using real-time particle counting and particle image velocimetry, decreased monotonically with the average bulk flux of phage through the membrane. At the pore scale, more phage bound in regions with faster local flow, confirming that both average and local flux increased binding. The number of bound phage increased with the aspect ratio of the phage and scaled with the phage surface area, consistent with a binding interaction controlled by the number of recognition elements on the surface. Together, these results indicate that increasing the likelihood that recognition elements on the surface of phage encounter the fibers enhances the assay binding efficiency and suggests one origin for the improved performance of nonspherical phage reporters.

A versatile platform for surface modification of microfluidic droplets

To advance emulsion droplet technology, we synthesize functional derivatives of Pluronic F127 that can simultaneously act as surfactants and as reactive sites for droplet surface decoration. The amine-, carboxyl-, N-hydroxysuccinimide ester-, maleimide- and biotin-terminated Pluronic F127 allows ligand immobilization on single-emulsion or double-emulsion droplets via electrostatic adsorption, covalent conjugation or site-specific avidin-biotin interaction.

Artificial Antigen-Presenting Cells for Immunotherapies

Artificial antigen-presenting cells (aAPCs) overcome many of the limitations of biologically based adoptive immunotherapy protocols. While these acellular systems can be designed with a variety of parameters, including material type, diameter, and proliferative signals for T cells, we outline methods to formulate and characterize a comprehensive polymeric microparticle aAPC platform. These aAPCs, which can be reproducibly fabricated in large quantities, efficiently stimulate antigen-specific T cell activation and proliferation by both paracrine cytokine signals and engagement of T cell surface proteins.

Laser-induced heating integrated with a microfluidic platform for real-time DNA replication and detection

This study developed a microfluidic platform for replicating and detecting DNA in real time by integrating a laser and a microfluidic device composed of polydimethylsiloxane. The design of the microchannels consisted of a laser-heating area and a detection area. An infrared laser was used as the heating source for DNA replication, and the laser power was adjusted to heat the solutions directly. In addition, strong biotin–avidin binding was used to capture and detect the replicated products. The biotin on one end was bound to avidin and anchored to the surface of the microchannels, whereas the biotin on the other end was bound to the quantum dots (Qdots). The results showed that the fluorescent intensity of the Qdots bound to the replicated products in the detection area increased with the number of thermal cycles created by the laser. When the number of thermal cycles was ≥10, the fluorescent intensity of the Qdots was directly detectable on the surface of the microchannels. The proposed method is more sensitive than detection methods entailing gel electrophoresis.

Applicability of avidin protein coated mesoporous silica nanoparticles as drug carriers in the lung

Mesoporous silica nanoparticles (MSNs) exhibit unique drug delivery properties and are thus considered as promising candidates for next generation nano-medicines. In particular, inhalation into the lungs represents a direct, non-invasive delivery route for treating lung disease. To assess MSN biocompatibility in the lung, we investigated the bioresponse of avidin-coated MSNs (MSN-AVI), as well as aminated (uncoated) MSNs, after direct application into the lungs of mice. We quantified MSN distribution, clearance rate, cell-specific uptake, and inflammatory responses to MSNs within one week after instillation. We show that amine-functionalized (MSN-NH2) particles are not taken up by lung epithelial cells, but induced a prolonged inflammatory response in the lung and macrophage cell death. In contrast, MSN-AVI co-localized with alveolar epithelial type 1 and type 2 cells in the lung in the absence of sustained inflammatory responses or cell death, and showed preferential epithelial cell uptake in in vitro co-cultures. Further, MSN-AVI particles demonstrated uniform particle distribution in mouse lungs and slow clearance rates. Thus, we provide evidence that avidin functionalized MSNs (MSN-AVI) have the potential to serve as versatile biocompatible drug carriers for lung-specific drug delivery.

A Highly Sensitive Immunosorbent Assay Based on Biotinylated Graphene Oxide and the Quartz Crystal Microbalance

A high-sensitivity flow-based immunoassay is reported based on a gold-coated quartz crystal microbalance (QCM) chip functionalized directly in the QCM without requiring covalent conjugation steps. Specifically, the irreversible adsorption of a biotinylated graphene oxide-avidin complex followed by loading of a biotinylated capture antibody is applied to avoid more complex conventional surface modification chemistries and enable chip functionalization and sensing all within the QCM instrument. The resulting immunosensors exhibit significantly lower nonspecific protein adsorption and stronger signal for antigen sensing relative to simple avidin-coated sensors. Reproducible quantification of rabbit IgG concentrations ranging from 0.1 ng/mL to 10 μg/mL (6 orders of magnitude) can be achieved depending on the approach used to quantify the binding with simple mass changes used to detect higher concentrations and a horseradish peroxidase-linked detection antibody that converts its substrate to a measurable precipitate used to detect very low analyte concentrations. Sensor fabrication and assay performance take ∼5 h in total, which is on par with or faster than other techniques. Quantitative sensing is possible in the presence of complex protein mixtures, such as human plasma. Given the broad availability of biotinylated capture antibodies, this method offers both an easy and flexible platform for the quantitative sensing of a variety of biomolecule targets.

Ion Mobility-Mass Spectrometry Reveals Highly-Compact Intermediates in the Collision Induced Dissociation of Charge-Reduced Protein Complexes

Protocols that aim to construct complete models of multiprotein complexes based on ion mobility and mass spectrometry data are becoming an important element of integrative structural biology efforts. However, the usefulness of such data is predicated, in part, on an ability to measure individual subunits removed from the complex while maintaining a compact/folded state. Gas-phase dissociation of intact complexes using collision induced dissociation is a potentially promising pathway for acquiring such protein monomer size information, but most product ions produced are possessed of high charge states and elongated/string-like conformations that are not useful in protein complex modeling. It has previously been demonstrated that the collision induced dissociation of charge-reduced protein complexes can produce compact subunit product ions; however, their formation mechanism is not well understood. Here, we present new experimental evidence for the avidin (64 kDa) and aldolase (157 kDa) tetramers that demonstrates significant complex remodeling during the dissociation of charge-reduced assemblies. Detailed analysis and modeling indicates that highly compact intermediates are accessed during the dissociation process by both complexes. Here, we present putative pathways that describe the formation of such ions, as well as discuss the broader significance of such data for structural biology applications moving forward.

The lifetime and attenuation properties measurements of a US/MR multimodality molecular probe

In our previous studies we explored the potential of using a combined US/magnetic resonance (MR) multimodality contrast agent, albumin-gadolinium-diethylenetriaminepentacetate (Gd-DTPA) MBs, to induce BBB opening and for distinguishing between FUS-induced BBB opening and intracerebral hemorrhage in MR T1-weighted contrast imaging. According to the previous study in the literature, 1-2 µm bubbles have more pronounced acoustic activity at frequencies above 10 MHz. The present study developed a new targeted US/MR multimodality MB and the acoustic properties were compared with two commercial MBs, SonoVue and Targestar SA. The acoustic activities of these 1.15-2.78 µm MBs with different shells at 10 MHz were investigated. The feasibility of designing a new targeted US/MR multimodality MB was investigated. The lifetime (survival of MBs in the liquid suspension) and attenuation properties of lipid MBs (SonoVue and Targestar SA), albumin-(Gd-DTPA) MBs, and avidin-conjugated albumin (avidin-albumin)-(Gd-DTPA) MBs at 10 MHz were investigated with the pulse-echo substitution method. It was found that incorporating avidin into the albumin MBs and avidin-albumin-(Gd-DTPA) MBs affects the size distribution but does not affect the concentration of MBs produced. The avidin-albumin-shelled MBs had more significant nonlinear activity at 4-18 MHz (p=0.025), while the nonlinear activity of the other MBs peaked at 6-24 MHz (p=0.003-0.044). Moreover, the incorporation of paramagnetic metal ions into the MB shells increased their attenuation coefficients. With regard to the lifetime of these agents, the attenuations of the SonoVue and Targestar SA lipid MBs were 87.96% and 8.74%, respectively, while those of albumin MBs, avidin-albumin MBs, albumin-(Gd-DTPA) MBs, and avidin-albumin-(Gd-DTPA) MBs were 49.52%, 41.38%, 74.69%, and 100%, respectively. Avidin conjugation decreased the lifetime of the albumin MBs, but not that of the lipid MBs. The incorporation of paramagnetic metal ions into the shells of albumin MBs did not decrease the lifetime.

[Radioimmunoimaging of lymphoma in mice with a two-step pretargeting strategy using biotinyled CD45 monoclonal antibody and (188)Re-avidin]

OBJECTIVE

To establish a two-step pretargeting approach to lymphoma radioimmunoimaging in mice using biotinynaled CD45 monoclonal antibody (McAb) and (188)Re-avidin in a tumor-bearing mouse model.

METHODS

Six Nod-Scid mice bearing lymphoma cell xenograft were randomized to receive either an intravenous injection of 50 µg/200 µL biotinyled CD45 McAb followed 24 h later by an intraperitoneal injection of 3.7 MBq (50 µg/100 µL) (188)Re-avidin (two-step pretargeting group), or a single intravenous injection of 3.7 MBq (100 µg/100 µL) (188)Re-CD45 McAb (control group). SPECT was performed at 0.5, 1, 6 and 23 h post-injection to characterize (188)Re isotope biodistribution. At 24 h pos-injection, the mice were sacrificed for measurement of radioactivity uptake in the tumor and normal tissues and calculation of the tumor-to-non-tumor (T/NT) ratios.

RESULTS

SPECT showed that the two-step pretargeting method resulted in a low radioactivity in the blood pool during the imaging and a concentrated radioactivity in the liver and spleen. The transplanted tumor began to be displayed at 1 h post-injection and was clearly displayed at 1-6 h; the images were clear even at 23 h. With the two-step pretargeting method, the radioactive uptake at 24 h post-injection were (1.34∓0.52)%, (6.77∓2.32)%, and (2.81∓1.25)% in the tumor, kidney and liver, respectively, with low radioactivity levels in other organs and high tumor/blood and tumor/muscle ratios (4.28∓0.82 and 8.00∓0.88, respectively). In the control group, SPECT revealed intense radioactivity in the liver, spleen, and kidneys with obscure display of the tumor; at 20 h, the radioactivity in the blood pool remained high but that in the tumor was low, and the tumor/blood and tumor/muscle ratios at 24 h were only 0.58∓0.06 and 3.21∓0.24, respectively.

CONCLUSION

Compared with (188)Re-CD45 McAb, the two-step pretargeting approach exhibits a good specificity in targeting lymphoma with an increased T/NT ratio in mice and allows early tumor display at 1 h post-injection.

[Establishment and diagnostic performance of biotin-avidin complex enzyme linked immunosorbent assay of detecting specific IgG4 of clonorchiasis]

OBJECTIVE

To explore the performance of the biotin-avidin complex enzyme linked immunosorbent assay of detecting specific IgG4 for the diagnosis of clonorchiasis.

METHODS

The avidin-biotin complex enzyme linked immunosorbent assay of detecting specific IgG4 (IgG4-ABC-ELISA)against Clonorchis sinensis was established, and used to detect the serum samples of patients with clonorchiosis sinensis, schistosomiasis japonica, paragonimiasis, toxoplasmosis, echinococcosis, cysticercosis and sparganosis mansoni. At the same time, these sera were analyzed by the ELISA of detecting IgG4 (IgG4-ELISA) and ELISA of detecting the total IgG (IgG-ELISA) as controls. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and the respective diagnostic performance of the three methods were compared.

RESULTS

The IgG4-ABC-ELISA for diagnosis of clonorchiasis was established successfully. The sensitivity and specificity of the IgG4-ABC-ELISA for detecting clonorchiasis were 90.0% and 98.2% respectively, and PPV and NPV were 93.8% and 97.0% respectively. Its diagnostic performance was 96.3%. The sensitivity and specificity of the IgG4-ELISA for detecting clonorchiasis were 86.0% and 98.2% respectively, and PPV and NPV were 93.5% and 95.9% respectively. Its diagnostic performance was 95.4%. The sensitivity and specificity of the IgG-ELISA for detecting clonorchiasis were 94.0% and 88.1% respectively, and PPV and NPV were 70.1% and 98.0% respectively. Its diagnostic performance was 89.4%. The sensitivity of IgG4-ABC-ELISA was higher than that of IgG4-ELISA (P < 0.05), and the specificity of IgG4-ABC-ELISA was higher than that of IgG-ELISA (P < 0.05).

CONCLUSIONS

IgG4-ABC-ELISA of detecting specific antibody IgG4 against Clonorchis sinensis has high sensitivity and specificity. Therefore, it has a good application value in the diagnosis of clonorchiasis.

Aptamer modification improves the adenoviral transduction of malignant glioma cells

Adenovirus has shown increasing promise in the gene-viral therapy for glioblastoma, a treatment strategy that relies on the delivery of viruses or transgenes into tumor cells. However, targeting of adenovirus to human glioblastoma remains a challenge due to the low expression level of coxsackie and adenovirus receptor (CAR) in glioma cells. Aptamers are small and highly structured single-stranded oligonucleotides that bind at high affinity to a target molecule, and are good candidates for targeted imaging and therapy. In this study, to construct an aptamer-modified Ad5, we first genetically modified the HVR5 of Ad hexon by biotin acceptor peptide (BAP), which would be metabolically biotinylated during production in HEK293 cells, and then attached the biotin labeled aptamer to the modified Ad through avidin–biotin binding. The aptamers used in this study includes AS1411 and GBI-10. The former is a DNA aptamer that can bind to nucleolin, a nuclear matrix protein found on the surface of cancer cells. The latter is a DNA aptamer that can recognize the extracellular matrix protein tenascin-C on the surface of human glioblastoma cells. To examine if aptamer-modification of the hexon protein could improve the adenoviral transduction efficiency, a glioblastoma cell line, U251, was transduced with aptamer-modified Ads. The transduction efficiency of AS1411- or GBI-10-modified Ad was approximately 4.1-fold or 5.2-fold higher than that of the control. The data indicated that aptamer modified adenovirus would be a useful tool for cancer gene therapy.

Honeycomb films of cellulose azide: molecular structure and formation of porous films

Development of value-added micropatterned porous materials from naturally abundant polymers, such as cellulose, are of growing interest. In this paper, regioselectively modified amphiphilic cellulose azide, 3-O-azidopropoxypoly(ethylene glycol)-2,6-di-O-thexyldimethylsilyl cellulose, with different degrees of substitution (DS) and degrees of polymerization (DP) of the poly(ethylene glycol) (PEG) side chain, was synthesized and employed in the formation of honeycomb-patterned films. With the variation of the DP and/or DS, the amphiphilicity of the polymer and the pore size of the formed films changed accordingly. It was found that amphiphilicity of the cellulose azide played a significant role in the formation of honeycomb films. Balanced amphiphilicity was of particular importance in the formation of uniform honeycomb films. Via the Cu(I)-catalyzed alkyne-azide [2 + 3] cycloaddition reaction, fluorescent avidin and quantum dots were attached to the films. By means of confocal microscopy, it was confirmed that the functional azido group was preferentially allocated inside the pores. This provides a platform for the development of advanced honeycomb materials with site-specific functionalities, such as biosensors.

[Establishment of BA-ELISA method for detecting CEA in human sera]

AIM

To establish a sensitive biotin-avidin enzyme linked immunosorbent assay (BA-ELISA) method for detecting carcinoembryonic antigen (CEA) in serum.

METHODS

CEA which had been purified by affinity chromatography was used to immunize the rabbits to produce polyclonal antibodies. Then the antibodies were connected with biotin and horseradish peroxidase (HRP). So BA-ELISA method was established on the basis of 96 microwell plates coated with biotinylated BSA. Finally we examined the sensitivity, specificity, stability and recovery rate of this system and compared the BA-ELISA method with the traditional ELISA, radioimmunoassay and chemiluminescence in detecting CEA concentrations.

RESULTS

The stability of this system was proved good. The linear range was from 0.42 to 50 U/mL, the sensitivity was 0.42 U/mL, and the intra-differences together with inter-differences were less than 10.0%. There was significant difference between BA-ELISA and traditional ELISA, while there was no significant difference between BA-ELISA and radioimmunoassay. The regression equation of this method was y=0.04825+0.99674x and r=0.994, and there was no significant difference between the BA-ELISA and chemiluminescence.

CONCLUSION

The BA-ELISA method we established to detect CEA was easy to operate, highly sensitive, low in price and suitable for application in clinical detection.

Determination of 3,4-dichlorinated biphenyl in soil samples by real-time immuno-PCR assay

A real-time fluorescent quantitative immuno-polymerase chain reaction (RT-IPCR) assay was developed for the detection of non-dioxin-like polychlorinated biphenyl (PCB) congener in soil samples. Based on the construction of 3,4-dichlorinated biphenyl (IUPAC PCB12) hapten and its immunogen, the specific polyclonal antibodies (pAbs) to PCB12 was obtained and used to develop a direct competitive RT-IPCR assay. Using the optimized assay, a standard curve for PCB12 was prepared. The linear range for the determination of PCB12 was from 10.0 to 1.0 x 106 fg/mL with a correlation coefficient of 0.98 and a detection limit of 1.53 fg/mL. The RT-IPCR assays were tested for their cross-reactivity profiles using four selected congeners and four Aroclor products. The results for the soil samples correlated with the concentrations of PCBs obtained by gas chromatography/mass spectrometry. This highly specific, sensitive, and robust assay can be applied to on-site tests of PCBs and serve as a model for other pollutant immunoassays.

Fluorescence signal enhancement of polydiacetylene vesicle stacks

Polydiacetylenes provide a good biological/chemical label-free detection system owing to their blue to red color change and fluorescence change from non-fluorescence to red fluorescence. One of the important factors to consider before applying polydiacetylenes to various sensors is to enhance the sensitivity against specific molecules. This paper reports two methods for stacking polydiacetylene vesicles for fluorescence signal enhancement of polydiacetylene on solid substrates. This focuses on how to achieve a highly sensitive sensor chip by introducing two strategies to immobilize the vesicles effectively on substrates. One method is layer-by-layer deposition through reactions of vesicles and avidins alternately on an avidin treated substrate. The other is to prepare a clustered vesicles solution by mixing the appropriate amount of a biotinylated vesicle solution and avidin solution, and then immobilize the clustered vesicles on the substrates. The former allows easy control of the layer thickness, whereas the latter can shorten the process time. These strategies can be applied to a range of biological/chemical sensors for fluorescence signal enhancement.

Tissue tropism of African horsesickness virus in the chicken embryo demonstrated with the avidin-biotin complex immunoperoxidase method

In horses, African horsesickness virus (AHSV) exhibits marked tropism for certain microvascular endothelia and components of the mononuclear phagocyte system. In this study, the tropism of a field isolate of AHSV serotype 5 was studied in 24 chicken embryos. Histopathology on embryonic tissues harvested with 12 hour intervals revealed progressive changes associated with endothelial damage. Immunolabeling demonstrated viral antigens in the microvascular endothelium of the spleen, lungs, and the mesenchymal connective tissue at the base of the neck, from 24 hours post inoculation. Subsequently, specific immunolabeling increased steadily in endothelia of these and other tissues such as skeletal and cardiac muscle, gastrointestinal smooth muscle, mesonephric glomeruli, liver, subcutis and feathers. Positive immunolabeling was also occasionally observed in circulating mononuclear cells and in Kupffer cells in the liver. It was concluded, that this isolate of AHSV displayed similar tissue tropism in the chicken embryo as in the horse.

One-step electrochemically deposited gold nanoparticles interface grafted with avidin for acetylcholinesterase biosensor design

In this study, an interface embedded in situ gold nanoparticles (AuNPs) and biotin in chitosan hydrogel was constructed by one-step electrochemical deposition in solution containing tetrachloroauric (III) acid, biotin and chitosan. This deposited interface acts as biosensing platforms and provides specific binding sites for avidin, which are further capable of attaching any biotinylated bimolecular for biosensor design. Atomic force microscopy (AFM), A.C. impedance and surface plasmon resonance were used to characterize this interface. The immobilized acetylcholinesterase (AChE), as a model, showed excellent activity to its substrate and provided a quantitative measurement of organophosphate pesticide. Under the optimal experimental conditions, the inhibition of dimethoate was proportional to its concentrations in the range of 0.05 to 15 microg mL(-1) with detection limit of 0.001 microg mL(-1). The simple method showed good fabrication reproducibility and acceptable stability, which provided a new avenue for electrochemical biosensor design.

UV-induced grafting processes with in situ formed photomask for micropatterning of two-component biomolecules

We report a photolithographic process for micropatterning of two-component biomolecules on a transparent organic film via lateral functional polymer brushes of poly(sodium acrylate) (P(AA)) and poly(glycidyl methacrylate) (P(GMA)). The pattern of binary polymer brushes were prepared via consecutive UV-initiated grafting processes, under the assistance of the in situ formed poly (4,4'-bi[N-(4-vinylbenzyl) pyridinium]) (P(BVV)) photomask. The epoxy groups of the P(GMA) microdomains can be aminated for covalently coupling biotin, while the P(AA) microdomains were used for immobilizing immunoglobulin (IgG). The resulting biotin- and IgG-coupled microdomains interact specifically with their corresponding target proteins, avidin and anti-IgG, respectively.

Spectroscopy on the wing: naturally inspired SERS substrates for biochemical analysis

We show that naturally occurring chitinous nanostructures found on the wings of the Graphium butterfly can be used as substrates for surface-enhanced Raman scattering when coated with a thin film of gold or silver. The substrates were found to exhibit excellent biocompatibility and sensitivity, making them ideal for protein assaying. An assay using avidin/biotin binding showed that the substrates could be used to quantify protein binding directly from changes in the surface-enhanced Raman scattering (SERS) spectra and were sensitive over a concentration range comparable with a typical enzyme-linked immunosorbent assays (ELISA) assay. A biomimetic version of the wing nanostructures produced using a highly reproducible, large-scale fabrication process, yielded comparable enhancement factors and biocompatibility. The excellent biocompatibility of the wings and biomimetic substrates is unparalleled by other lithographically produced substrates, and this could pave the way for widespread application of ultrasensitive SERS-based bioassays.

[Clinical application of avidin-biotin ELISA to detect serum hepatoma-specific gamma-glutamyltransferase in patients with primary hepatic cancer]

OBJECTIVE

To detect serum hepatoma-specific datura stramonium lectin-tightly binding gamma-glutamyl transferase (DSA-GGT) in patients with primary hepatic cancer (PHC) by avidin-biotin ELISA method which was established in our laboratory, and carry on a study of its clinical application.

METHODS

To detect serum DSA-GGT in 45 healthy control subjects, 58 PHC patients and 203 non-PHC patients (including 36 patients with other tumors and 167 patients with benign liver diseases) with the method was established; meanwhile, AFP was detected by ELISA method.

RESULTS

38 individuals were DSA-GGT positive in 58 PHC patients, the sensitivity was 65.5%. 18 individuals were DSA-GGT positive in 203 patients without PHC, the specificity was 91.1%. The sensitivity and specificity of AFP in diagnosis of PHC patients was 69.0% and 90.6%, respectively. The sensitivity and specificity of combination of DSA-GGT and AFP was 93.1% and 85.7%, respectively. The average intra-CV and inter-CV of DSA-GGT ELISA was 8.9% and 11.5%, respectively.

CONCLUSION

The sensitivity and specificity of DSA-GGT ELISA method established in our lab is similar with that of AFP assay and the accuracy is good. Combination of DSA-GGT and AFP may improve the diagnostic sensitivity. The method should be potentially as a new way to improve diagnosis of PHC.

Vector retargeting for cancer gene therapy

Vector tropism is a research hot spot in cancer gene therapy, and targeted viral vectors play a key role in the enhancement of safety and efficiency in cancer gene therapy. Vector retargeting is one of the important strategies on viral vector targeting. This review mainly focused on the progresses of vector retargeting in cancer gene therapy, and summarized relevant pathways and strategies.

Enhanced cytotoxicity of an anti-transferrin receptor IgG3-avidin fusion protein in combination with gambogic acid against human malignant hematopoietic cells: functional relevance of iron, the receptor, and reactive oxygen species

The human transferrin receptor (hTfR) is a target for cancer immunotherapy due to its overexpression on the surface of cancer cells. We previously developed an antibody-avidin fusion protein that targets hTfR (anti-hTfR IgG3-Av) and exhibits intrinsic cytotoxicity against certain malignant cells. Gambogic acid (GA), a drug that also binds hTfR, induces cytotoxicity in several malignant cell lines. We now report that anti-hTfR IgG3-Av and GA induce cytotoxicity in a new broader panel of hematopoietic malignant cell lines. Our results show that the effect of anti-hTfR IgG3-Av is iron-dependent whereas that of GA is iron-independent in all cells tested. In addition, we observed that GA exerts a TfR-independent cytotoxicity. We also found that GA increases the generation of reactive oxygen species that may play a role in the cytotoxicity induced by this drug. Additive cytotoxicity was observed by simultaneous combination treatment with these drugs and synergy by using anti-hTfR IgG3-Av as a chemosensitizing agent. In addition, we found a concentration of GA that is toxic to malignant hematopoietic cells but not to human hematopoietic progenitor cells. Our results suggest that these two compounds may be effective, alone or in combination, for the treatment of human hematopoietic malignancies.

Detection and quantitation of the activity of DNA methyltransferases using a biotin/avidin microplate assay

The biotin-avidin microplate assay is a sensitive method to measure methylation of biotinylated oligonucleotide substrates by DNA methyltransferases (MTases). The methylation reaction is carried out in solution using [methyl-3H]-AdoMet. Afterwards, the oligonucleotides are immobilized on an avidin-coated microplate, where the incorporation of [3H]-labeled methyl groups into the DNA is stopped by addition of unlabeled AdoMet to the binding buffer. Separation of radioactively labeled DNA from unreacted AdoMet and enzyme is performed by washing steps. Subsequently, the radioactivity incorporated into the DNA is released by a nucleolytic digestion of the DNA. By liquid scintillation counting, the amount of DNA methylation can be determined. Advantages of the microplate assay are its high sensitivity which allows the detection of low amounts of DNA methylation, the efficient separation of reaction components resulting in a low background of radioactivity and a high accuracy (+/-10%) and reliability. Furthermore, the assay is very convenient, fast and well suited for automation.

Pseudo-immunolabelling with the avidin-biotin-peroxidase complex due to the presence of endogenous biotin in the retina

Immunodetection techniques are dependent on enzyme-protein conjugates for the visualization of antigen-antibody complexes. One of the most widely used is the avidin-biotin-peroxidase complex (ABC) method. However, treatment of certain tissues with ABC reagents alone may result in high background, which is indicative for the presence of endogenous biotin or biotinylated proteins. In goldfish and salamander retinal sections, we observed a distinct staining pattern, presumably through binding of avidin to endogenous biotin in Müller cells. These findings summon for caution in the application of detection systems based on biotinylated antibodies or biotinylated DNA probes.

Evaluation of Indirect and Avidin–Biotin Enzyme Linked Immunosorbent Assays for Detection of Anti-Listeriolysin O Antibodies in Bovine Milk Samples

Listeria monocytogenes is a foodborne pathogen that causes a wide spectrum of diseases in humans and animals. Enzyme linked immunosorbent assays (ELISA) [indirect and avidin-biotin (A-B)] for detecting L. monocytogenes antibodies in bovine milk samples (n = 2060) were standardized and evaluated by comparison with bacteriological examination. The tests were standardized by checker board titration. Highly purified listeriolysin O (LLO) was used as an antigen. Receiver operating characteristic (ROC) analysis was performed to decide the cut-off values. The ROC analysis revealed the sensitivities of indirect and A-B ELISA as 100% and specificities as 97.1 and 99.9% respectively. Listeria monocytogenes was isolated from 105 (5.1%) milk samples collected from 52 farms. Anti-LLO IgG antibodies were detected from 137 and 112 milk samples when tested by indirect and A-B ELISA respectively. Of the 52 farms screened, 28 (53.8%) yielded one or more isolates of L. monocytogenes and 33 (63.5%) of the farms had one or more animals simultaneously positive by one or both the assays for anti-LLO antibodies.