Avidin-Biotin Technology in Gold Nanoparticle-Decorated Graphene Field Effect Transistors for Detection of Biotinylated Macromolecules with Ultrahigh Sensitivity and Specificity

D-(+)-Biotinylated squaraine dyes: A journey from synthetic conception, photophysical and -chemical characterization, to the exploration of their photoantitumoral action mechanisms

Biotin is primarily taken up by cells through sodium-dependent multivitamin transporter, which is highly expressed in aggressive cancer cell lines, often at levels surpassing those of the folate receptor. This makes biotin an attractive ligand for tumor-targeted drug delivery. Building on this rationale, this study presents a series of six D-(+)-biotin-conjugated squaraine dyes derived from benzothiazole, indolenine, and benz[e]indole, with N-ethyl and N-hexyl chains. These compounds were thoroughly characterized in terms of their photophysical and photochemical properties, revealing strong absorption in the so-called "phototherapeutic window", notable fluorescence, especially the benzothiazole derivatives, aqueous stability, particularly the indolenine-based dyes, and moderate to high photostability. Computational studies further indicated a strong binding affinity to human serum albumin and avidin proteins. All dyes exhibited photodynamic activity, with indolenine derivatives showing remarkable tumor selectivity and benz[e]indole analogs evidencing superior photocytotoxicity. The most promising compounds preferentially accumulated in mitochondria, and both singlet oxygen and other reactive oxygen species were found to play a role in their photobiological effects. Additionally, they were non-genotoxic in the absence of irradiation, and apoptosis was the primary mechanism of cell death upon light activation. This was evidenced by preserved cytoplasmic membrane integrity, nuclear fragmentation, and caspase-3/7 activation, reinforcing the safety and potential of these compounds as phototherapeutic agents. Although cellular uptake via the sodium-dependent multivitamin transporter was not established, and diffusion is expected to be the predominant mechanism, the high predicted avidin-binding affinity of these dyes opens exciting new avenues for photodynamic therapy-combined strategies.

Design of innovative and low-cost dopamine-biotin conjugate sensor for the efficient detection of protein and cancer cells

The rapid, precise identification and quantification of specific biomarkers, toxins, or pathogens is currently a key strategy for achieving more efficient diagnoses. Herein a dopamine-biotin monomer was synthetized and oxidized in the presence of hexamethylenediamine, to obtain adhesive coatings based on polydopamine-biotin (PDA-BT) on different materials to be used in targeted molecular therapy. Insight into the structure of the PDA-BT coating was obtained by solid-state 13C NMR spectroscopy acquired, for the first time, directly onto the coating, deposited on alumina spheres. The receptor binding capacity of the PDA-BT coating toward 4-hydroxyazobenzene-2-carboxylic acid/Avidin complex was verified by means of UV-vis spectroscopy. Different deposition cycles of avidin onto the PDA-BT coating by layer-by-layer assembly showed that the film retains its receptor binding capacity for at least eight consecutive cycles. Finally, the feasibility of PDA-BT coating to recognize cell lines with different grade of overexpression of biotin receptors (BR) was investigated by tumor cell capture experiments by using MCF-7 (BR+) and HL-60 (BR-) cell lines. The results show that the developed system can selectively capture MCF-7 cells indicating that it could represent a first approach for the development of future more sophisticated biosensors easily accessible, low cost and recyclable with the dual and rapid detection of both proteins and cells.

A one-process production of completely biotinylated proteins in a T7 expression system

Streptavidin is a tetrameric protein with high specificity and affinity for biotin. The interaction between avidin and biotin has become a valuable tool in nanotechnology. In recent years, the site-specific biotin modification of proteins using biotin ligases, such as BirA, has attracted attention. This study established an in vivo method for achieving the complete biotinylation of target proteins using a single plasmid co-expressing BirA and its target proteins. Specifically, a biotin-modified protein was produced in Escherichia coli strain BL21(DE3) using a single plasmid containing genes encoding both BirA and a protein fused to BirA's substrate sequence, Avitag. This approach simplifies the production of biotinylated proteins in E. coli and allows the creation of various biotinylated protein types through gene replacement. Furthermore, the biotin modification rate of the obtained target protein could be evaluated using Native-PAGE without performing complicated isolation operations of biotinylated proteins. In Native-PAGE, biotin-modified proteins and unmodified proteins were confirmed as clearly different bands, and it was possible to easily derive the modification rate from the respective band intensities.

Ultra-sensitive nitrate-ion detection via transconductance-enhanced graphene ion-sensitive field-effect transistors

Current potentiometric sensing methods are limited to detecting nitrate at parts-per-billion (sub-micromolar) concentrations, and there are no existing potentiometric chemical sensors with ultralow detection limits below the parts-per-trillion (picomolar) level. To address these challenges, we integrate interdigital graphene ion-sensitive field-effect transistors (ISFETs) with a nitrate ion-sensitive membrane (ISM). The work aims to maximize nitrate ion transport through the nitrate ISM, while achieving high device transconductance by evaluating graphene layer thickness, optimizing channel width-to-length ratio (RWL), and enlarging total sensing area. The captured nitrate ions by the nitrate ISM induce surface potential changes that are transduced into electrical signals by graphene, manifested as the Dirac point shifts. The device exhibits Nernst response behavior under ultralow concentrations, achieving a sensitivity of 28 mV/decade and establishing a record low limit of detection of 0.041 ppt (4.8 × 10-13 M). Additionally, the sensor showed a wide linear detection range from 0.1 ppt (1.2 × 10-12 M) to 100 ppm (1.2 × 10-3 M). Furthermore, successful detection of nitrate in tap and snow water was demonstrated with high accuracy, indicating promising applications to drinking water safety and environmental water quality control.

Ultrasensitive detection of 5-hydroxymethylcytosine in genomic DNA using a graphene-based sensor modified with biotin and gold nanoparticles

Ten-eleven translocation (TET) proteins orchestrate deoxyribonucleic acid (DNA) methylation-demethylation dynamics by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine (5hmC) and are frequently inactivated in various cancers. Due to the significance of 5hmC as an epigenetic biomarker for cancer diagnosis, pathogenesis, and treatment, its rapid and precise quantification is essential. Here, we report a highly sensitive electrochemical method for quantifying genomic 5hmC using graphene sheets that were electrochemically exfoliated and functionalized with biotin and gold nanoparticles (Bt-AuNPs) through a single-step electrical method. The attachment of Bt-AuNPs to graphene enhances the specificity of 5hmC-containing DNA and augments the oxidation of 5hmC to 5-formylcytosine in DNA. When coupled to a gold electrode, the Bt-AuNP-graphene-based sensor exhibits exceptional sensitivity and specificity for detecting 5hmC, with a detection limit of 63.2 fM. Furthermore, our sensor exhibits a remarkable capacity to measure 5hmC levels across a range of biological samples, including preclinical mouse tissues with varying 5hmC levels due to either TET gene disruption or oncogenic transformation, as well as human prostate cancer cell lines. Therefore, our sensing strategy has substantial potential for cancer diagnostics and prognosis.

Biotin-functionalized nanoparticles: an overview of recent trends in cancer detection

Electrochemical bio-sensing is a potent and efficient method for converting various biological recognition events into voltage, current, and impedance electrical signals. Biochemical sensors are now a common part of medical applications, such as detecting blood glucose levels, detecting food pathogens, and detecting specific cancers. As an exciting feature, bio-affinity couples, such as proteins with aptamers, ligands, paired nucleotides, and antibodies with antigens, are commonly used as bio-sensitive elements in electrochemical biosensors. Biotin-avidin interactions have been utilized for various purposes in recent years, such as targeting drugs, diagnosing clinically, labeling immunologically, biotechnology, biomedical engineering, and separating or purifying biomolecular compounds. The interaction between biotin and avidin is widely regarded as one of the most robust and reliable noncovalent interactions due to its high bi-affinity and ability to remain selective and accurate under various reaction conditions and bio-molecular attachments. More recently, there have been numerous attempts to develop electrochemical sensors to sense circulating cancer cells and the measurement of intracellular levels of protein thiols, formaldehyde, vitamin-targeted polymers, huwentoxin-I, anti-human antibodies, and a variety of tumor markers (including alpha-fetoprotein, epidermal growth factor receptor, prostate-specific Ag, carcinoembryonic Ag, cancer antigen 125, cancer antigen 15-3, etc.). Still, the non-specific binding of biotin to endogenous biotin-binding proteins present in biological samples can result in false-positive signals and hinder the accurate detection of cancer biomarkers. This review summarizes various categories of biotin-functional nanoparticles designed to detect such biomarkers and highlights some challenges in using them as diagnostic tools.

Review on two-dimensional material-based field-effect transistor biosensors: accomplishments, mechanisms, and perspectives

Field-effect transistor (FET) is regarded as the most promising candidate for the next-generation biosensor, benefiting from the advantages of label-free, easy operation, low cost, easy integration, and direct detection of biomarkers in liquid environments. With the burgeoning advances in nanotechnology and biotechnology, researchers are trying to improve the sensitivity of FET biosensors and broaden their application scenarios from multiple strategies. In order to enable researchers to understand and apply FET biosensors deeply, focusing on the multidisciplinary technical details, the iteration and evolution of FET biosensors are reviewed from exploring the sensing mechanism in detecting biomolecules (research direction 1), the response signal type (research direction 2), the sensing performance optimization (research direction 3), and the integration strategy (research direction 4). Aiming at each research direction, forward perspectives and dialectical evaluations are summarized to enlighten rewarding investigations.

Streptavidin Fe2O3-gold nanoparticles functionalized theranostic liposome for antibiotic resistant bacteria and biotin sensing

Novel methods of sensing and treatment required to elicit potent humoral and cellular immune responses. Here, Streptavidin functionalized α-Fe2O3-Au nanoparticles (STV-Mag) loaded cationic carbomate cholesterol is used as a carrier to release antibacterial thymol drug for Staphylococcus aureus (S. aureus) infected Caenorhabditis elegans (C. elegans). Pertaining to theranostic applications, efficient antimicrobial activity, and non-stimulated drug release and biotin dependent S. aureus growth were studied in-vivo. While STV-Mag was tethered on mercaptobenzoic acid (MBA) molecular cushion for label free streptavidin-biotin electrochemical sensing, the STV-Mag-carbomate cholesterol (STV-Mag-cCHOL liposome) vesicle with loaded drug was tethered on MBA for non-stimulant drug release through specific cholesterol-S. aureus interaction and confirmed electrochemically. Selectivity was confirmed using other pathogens, E. coli, Proteus and Enterococcus bacterium through antimicrobial studies along with S. aureus. The biotin sensing showed linear range from 10-15 to 10-3 M, which was not obtained by conventional methods. Fourier-Transform Infra-red (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques were used to characterize the nanoparticulate system.

SARS-CoV-2 Tests: Bridging the Gap between Laboratory Sensors and Clinical Applications

This review covers emerging biosensors for SARS-CoV-2 detection together with a review of the biochemical and clinical assays that are in use in hospitals and clinical laboratories. We discuss the gap in bridging the current practice of testing laboratories with nucleic acid amplification methods, and the robustness of assays the laboratories seek, and what emerging SARS-CoV-2 sensors have currently addressed in the literature. Together with the established nucleic acid and biochemical tests, we review emerging technology and antibody tests to determine the effectiveness of vaccines on individuals.

Advances in Drug Delivery Nanosystems Using Graphene-Based Materials and Carbon Nanotubes

Carbon is one of the most abundant elements on Earth. In addition to the well-known crystallographic modifications such as graphite and diamond, other allotropic carbon modifications such as graphene-based nanomaterials and carbon nanotubes have recently come to the fore. These carbon nanomaterials can be designed to help deliver or target drugs more efficiently and to innovate therapeutic approaches, especially for cancer treatment, but also for the development of new diagnostic agents for malignancies and are expected to help combine molecular imaging for diagnosis with therapies. This paper summarizes the latest designed drug delivery nanosystems based on graphene, graphene quantum dots, graphene oxide, reduced graphene oxide and carbon nanotubes, mainly for anticancer therapy.

Carbon-Dot-Enhanced Graphene Field-Effect Transistors for Ultrasensitive Detection of Exosomes

Graphene field-effect transistors (GFETs) are suitable building blocks for high-performance electrical biosensors, because graphene inherently exhibits a strong response to charged biomolecules on its surface. However, achieving ultralow limit-of-detection (LoD) is limited by sensor response time and screening effect. Herein, we demonstrate that the detection limit of GFET biosensors can be improved significantly by decorating the uncovered graphene sensor area with carbon dots (CDs). The developed CDs-GFET biosensors used for exosome detection exhibited higher sensitivity, faster response, and three orders of magnitude improvements in the LoD compared with nondecorated GFET biosensors. A LoD down to 100 particles/μL was achieved with CDs-GFET sensor for exosome detection with the capability for further improvements. The results were further supported by atomic force microscopy (AFM) and fluorescent microscopy measurements. The high-performance CDs-GFET biosensors will aid the development of an ultrahigh sensitivity biosensing platform based on graphene for rapid and early diagnosis of diseases.