Influence of carbon nanodots on DNA-Thionine interaction. Application to breast cancer diagnosis

Modern Electrochemical Biosensing Based on Nucleic Acids and Carbon Nanomaterials

To meet the requirements of novel therapies, effective treatments should be supported by diagnostic tools characterized by appropriate analytical and working parameters. These are, in particular, fast and reliable responses that are proportional to analyte concentration, with low detection limits, high selectivity, cost-efficient construction, and portability, allowing for the development of point-of-care devices. Biosensors using nucleic acids as receptors has turned out to be an effective approach for meeting the abovementioned requirements. Careful design of the receptor layers will allow them to obtain DNA biosensors that are dedicated to almost any analyte, including ions, low and high molecular weight compounds, nucleic acids, proteins, and even whole cells. The impulse for the application of carbon nanomaterials in electrochemical DNA biosensors is rooted in the possibility to further influence their analytical parameters and adjust them to the chosen analysis. Such nanomaterials enable the lowering of the detection limit, the extension of the biosensor linear response, or the increase in selectivity. This is possible thanks to their high conductivity, large surface-to-area ratio, ease of chemical modification, and introduction of other nanomaterials, such as nanoparticles, into the carbon structures. This review discusses the recent advances on the design and application of carbon nanomaterials in electrochemical DNA biosensors that are dedicated especially to modern medical diagnostics.

Thionine-mediated electrocatalytic reduction for electrochemical detection of EDTA-Fe(III) in soy sauce

Electrocatalytic reactions based on electron transfer mediators provide a simple and effective route for the development of convenient and sensitive electrochemical assays. Here, we report a novel electrocatalytic assay for detection of EDTA-Fe(III), which is widely used as a supplement in iron-fortified foods to reduce prevalence of iron deficiency. Unlike conventional electrochemical methods to detect Fe(III) ion, signaling mechanism of our electrocatalytic assay relies on the previously unexplored thionine-mediated electrochemical reduction of EDTA-Fe(III). This electrocatalytic detection method is sensitive for EDTA-Fe(III) detection in the linear concentration range from 10 to 750 μM with a detection limit of 2.5 μM. It is also specific enough and applicable to detection of EDTA-Fe(III) in real soy sauce samples with satisfactory recovery. The one-step electrocatalytic reduction for signal generation enables the direct and sensitive electrochemical detection of EDTA-Fe(III). We believe that this electrocatalytic assay can serve as a general platform for quantification of EDTA-Fe(III) in many EDTA-Fe(III)-fortified foods. And because thionine is increasingly used as a signal reporter in electrochemical DNA/aptamer sensors, the engineered electrocatalytic reaction of thionine-mediated electrochemical reduction of EDTA-Fe(III) will also provide a simple signal amplification means for the development of highly sensitive electrochemical biosensors.

Dynamic interplay between thionine and DNA under carbon ion irradiation: a real-time first-principles study

Understanding the interactions between deoxyribonucleic acid (DNA) and photosensitizer under ion irradiation benefits the development of aptasensors, DNA biosensors and cancer diagnosis. Using real-time time-depended density functional theory, by simulating high-energy C ion passing through DNA with poly(dG)·poly(dC) sequence and that with embedded thionine (3,7-diamino-5-phenothiazinium, TH), we compared the electronic stopping power (ESP), evolution of the structure and charge, and absorption spectrum. TH inserting leads the increase in space charge density, a larger electron de-excitation and a larger ESP, but the speed corresponding to the maximum ESP is almost same. When C ion passes through TH-DNA, the structure of TH slightly changes and there still exists noncovalent interaction between TH and DNA, but the absorption coefficient depends on the electron occupied state of TH when the ion passes through. These results indicate that at low radiation doses, TH still can be a DNA detector, although its response wavelength and intensity have been slightly changed, and provide a theoretical reference to improve the possible application of phenothiazine dye in DNA biosensor under ion irradiation.

Methylene Blue functionalized carbon nanodots combined with different shape gold nanostructures for sensitive and selective SARS-CoV-2 sensing

The development of DNA-sensing platforms based on new synthetized Methylene Blue functionalized carbon nanodots combined with different shape gold nanostructures (AuNs), as a new pathway to develop a selective and sensitive methodology for SARS-CoV-2 detection is presented. A mixture of gold nanoparticles and gold nanotriangles have been synthetized to modify disposable electrodes that act as an enhanced nanostructured electrochemical surface for DNA probe immobilization. On the other hand, modified carbon nanodots prepared a la carte to contain Methylene Blue (MB-CDs) are used as electrochemical indicators of the hybridization event. These MB-CDs, due to their structure, are able to interact differently with double and single-stranded DNA molecules. Based on this strategy, target sequences of the SARS-CoV-2 virus have been detected in a straightforward way and rapidly with a detection limit of 2.00 aM. Moreover, this platform allows the detection of the SARS-CoV-2 sequence in the presence of other viruses, and also a single nucleotide polymorphism (SNPs). The developed approach has been tested directly on RNA obtained from nasopharyngeal samples from COVID-19 patients, avoiding any amplification process. The results agree well with those obtained by RT-qPCR or reverse transcription quantitative polymerase chain reaction technique.

Study on visible light photocatalytic performance of MIL-100(Fe) modified by carbon nanodots

The emerging porous material metal organic framework (MOFs) has caught researchers' attention in the field of photocatalysis. In this study, a visible light-driven carbon nanodots/MIL-100(Fe) photocatalytic material was prepared by in situ synthesis method. The study found that the composite material loaded with 2.5 mg C-dots (2.5-carbon nanodots/MIL-100(Fe)) showed the best tetracycline degradation efficiency with 4.2 times higher than that of MIL-100(Fe) materials in a neutral environment. The superiority of 2.5-carbon nanodots/MIL-100(Fe) in degrading tetracycline is attributed to the fact that C-dots have the ability to act as acceptors and donors of electrons, thus promoting electron transfer and inhibiting electron-hole recombination. Moreover, the 2.5-carbon nanodots/MIL-100(Fe) also showed high stability after five cycles of the photodegradation reaction. The quenching experiment proved that the main active substances that degrade tetracycline were O₂^- and h⁺. The study of carbon nanodots /MIL-100(Fe) composite materials provides new thoughts and methods for the removal of organic pollutants.

A nanomaterial-free and thionine labeling-based lateral flow immunoassay for rapid and visual detection of the transgenic CP4-EPSPS protein

Nanomaterial-based lateral flow immunoassays (LFIAs) have been widely used for the on-site detection of genetically modified components. However, the practical applications are often limited by the complex matrix, such as in red samples. In this study, a thionine (Thi) labeling-based LFIA was developed for the first time to detect CP4-EPSPS protein. The optimal labeling concentration of Thi was 0.5 mg/mL, and the antibody could be rapidly coupled to Thi in 10 min. The visual limit of detection (vLOD) levels for transgenic soybean, sugar beet, and cotton containing the CP4-EPSPS protein reached 0.05%, 0.1%, and 0.1%, respectively, and had no interference from other proteins. After storage at 4 °C for three months, the LFIA sensitivity remained unchanged and showed good stability. This method could be used to screen and detect a variety of transgenic crops containing the CP4-EPSPS protein, and the results were consistent with the current standard assay. This study pioneered the development of an immunochromatographic method using Thi as a marker and applied it to the detection of the CP4-EPSPS protein in herbicide-tolerant transgenic crops. This provides a new method for the rapid immunoassay of Thi as a dye and has good prospects for practical application.

A Label-Free Immunosensor Based on Gold Nanoparticles/Thionine for Sensitive Detection of PAT Protein in Genetically Modified Crops

Genetically modified (GM) crops containing phosphinothricin acetyltransferase (PAT) protein has been widely planted worldwide. The development of a rapid method for detecting PAT protein is of great importance to food supervision. In this study, a simple label-free electrochemical immunosensor for the ultrasensitive detection of PAT protein was constructed using thionine (Thi)/gold nanoparticles (AuNPs) as signal amplification molecules and electrochemically active substances. Under optimum conditions, the limits of detection of the sensor for soybean A2704-12 and maize BT-176 were 0.02% and 0.03%, respectively. The sensor could detect crops containing PAT protein and had no cross-reaction with other proteins. After storage at 4°C for 33 days, the sensor still retained 82.5% of the original signal, with a relative standard deviation (RSD) of 0.92%. The recoveries of the sensor for soybean A2704-12 and maize BT-176 were 85%-108% and 98%-113%, respectively. The developed PAT-target immunosensor with high sensitivity, specificity, and satisfactory reproducibility and accuracy will be a useful tool in the trace screening of GM crops. Moreover, this design concept can be extended to other proteins by simply changing the antibody.

A MoS2 platform and thionine-carbon nanodots for sensitive and selective detection of pathogens

This work focuses on the combination of molybdenum disulfide (MoS₂) and à la carte functionalized carbon nanodots (CNDs) for the development of DNA biosensors for selective and sensitive detection of pathogens. MoS₂ flakes prepared through liquid-phase exfoliation, serves as platform for thiolated DNA probe immobilization, while thionine functionalized carbon nanodots (Thi-CNDs) are used as electrochemical indicator of the hybridization event. Spectroscopic and electrochemical studies confirmed the interaction of Thi-CNDs with DNA. As an illustration of the pathogen biosensor functioning, DNA sequences from InIA gen of Listeria monocytogenes bacteria and open reading frame sequence (ORF1ab) of SARS-CoV-2 virus were detected and quantified with a detection limit of 67.0 fM and 1.01 pM, respectively. Given the paradigmatic selectivity of the DNA hybridization, this approach allows pathogen detection in the presence of other pathogens, demonstrated by the detection of Listeria monocytogenes in presence of Escherichia coli. We note that this design is in principle amenable to any pathogen for which the DNA has been sequenced, including other viruses and bacteria. As example of the application of the method in real samples it has been used to directly detect Listeria monocytogenes in cultures without any DNA Polymerase Chain Reaction (PCR) amplification process.

Nanostructured graphitic carbon nitride based ultrasensing electrochemical biosensor for food toxin detection

We report results of the studies related to the fabrication of thionine functionalized graphitic carbon nitride nanosheets based ultrasensing platform for food toxin (Aflatoxin B1, AfB₁) detection. The synthesis of graphitic carbon nitride nanosheets (g-C₃N₄) was carried out by polycondensation of melamine followed by chemical exfoliation. Further, thionine was used for the functionalization of g-C₃N₄ (Thn/g-C₃N₄) and deposited electrophoretically onto the indium tin oxide (ITO) coated glass electrode. The fabricated Thn/g-C₃N₄/ITO electrode was covalently immobilized by EDC-NHS chemistry with anti-aflatoxin B1 (anti-AfB₁) followed by blocking of non-specific sites using BSA molecules. For structural, morphological, functional and electrochemical properties analysis of synthesized nanomaterials and fabricated electrodes X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, atomic force microscopy and cyclic voltammetry techniques were used. The electrochemical response studies of the fabricated biosensing platform (BSA/anti-AfB₁/Thn/g-C₃N₄/ITO) were carried out towards detection of AfB₁ antigen using cyclic voltammetry technique. The obtained electrochemical results indicate that the fabricated biosensing electrode having ability to detect AfB₁ with lower limit of detection of 0.328 fg mL^-1, linear detection range in between 1 fg mL^-1 to 1 ng mL^-1, sensitivity of 4.85 μA log [ng^-1 mL] cm^-2 with stability upto 7 weeks.

Electrochemiluminescence Biosensors Using Screen-Printed Electrodes

Electrogenerated chemiluminescence (also called electrochemiluminescence (ECL)) has become a great focus of attention in different fields of analysis, mainly as a consequence of the potential remarkably high sensitivity and wide dynamic range. In the particular case of sensing applications, ECL biosensor unites the benefits of the high selectivity of biological recognition elements and the high sensitivity of ECL analysis methods. Hence, it is a powerful analytical device for sensitive detection of different analytes of interest in medical prognosis and diagnosis, food control and environment. These wide range of applications are increased by the introduction of screen-printed electrodes (SPEs). Disposable SPE-based biosensors cover the need to perform in-situ measurements with portable devices quickly and accurately. In this review, we sum up the latest biosensing applications and current progress on ECL bioanalysis combined with disposable SPEs in the field of bio affinity ECL sensors including immunosensors, DNA analysis and catalytic ECL sensors. Furthermore, the integration of nanomaterials with particular physical and chemical properties in the ECL biosensing systems has improved tremendously their sensitivity and overall performance, being one of the most appropriates research fields for the development of highly sensitive ECL biosensor devices.