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Ferrocene or ferrocenium has been widely studied in the field of organometallic complexes because of its stable thermodynamic, kinetic and redox properties. Novel hexaferrocenium tri[hexa(isothiocyanato)iron(III)]trihydroxonium (HexaFc) complex was the product from the reaction of ferrocene, maleic acid and ammonium thiocyanate and was confirmed by elemental analysis CHNS, FTIR and single crystal X-ray crystallography. In this study, HexaFc was used for the first time as an electroactive indicator for porcine DNA biosensor. The UV-Vis DNA titrations with this compound showed hypochromism and redshift at 250 nm with increasing DNA concentrations. The binding constant (K b ) for HexaFc complex towards CT-DNA (calf-thymus DNA) was 3.1 × 10 4  M -1 , indicated intercalator behaviour of the complex. To test the usefulness of this complex for DNA biosensor application, a porcine DNA biosensor was constructed. The recognition probes were covalently immobilised onto silica nanospheres (SiNSs) via glutaraldehyde linker on a screen-printed electrode (SPE). After intercalation with the HexaFc complex, the response of the biosensor to the complementary porcine DNA was measured using differential pulse voltammetry. The DNA biosensor demonstrated a linear response range to the complementary porcine DNA from 1 × 10 -6 to 1 × 10 -3  µM (R 2  = 0.9642) with a limit detection of 4.83 × 10 -8  µM and the response was stable up to 23 days of storage at 4 °C with 86% of its initial response. The results indicated that HexaFc complex is a feasible indicator for the DNA hybridisation without the use of a chemical label for the detection of porcine DNA.

A toxicity electrochemical DNA biosensor has been constructed for the detection of carcinogens using 24 base guanine DNA rich single stranded DNA, and methylene blue (MB) as the electroactive indicator. This amine terminated ssDNA was immobilized onto silica nanospheres and deposited on gold nanoparticle modified carbon-paste screen printed electrodes (SPEs). The modified SPE was initially exposed to a carcinogen, followed by immersion in methylene blue for an optimized duration. The biosensor response was measured using differential pulse voltammetry. The performance of the biosensor was identified on several anti-cancer compounds. The toxicity DNA biosensor demonstrated a linear response range to the cadmium chloride from 0.0005 ppm to 0.01 ppm (R 2 = 0.928) with a limit of detection at 0.0004 ppm. The biosensor also exhibited its versatility to screen the carcinogenicity of potential anti-cancer compounds.

[Display omitted] • An electrochemical DNA biosensor has been effectively developed based on polyacrylic microspheres and gold nanoparticles (AuNPs) for the identification of the gene sequence of the harmful microalgae Alexandrium minutum. • Anthraquinone-2-sulfonic acid derivative (AQMS) works as a specific indicator for redox DNA hybridisation, enabling the identification of the harmful microalgae Alexandrium minutum for the first time. • The DNA biosensor, employing AQMS as a redox label for the detection of Alexandrium minutum demonstrated a minimal limit of detection and possessed an extensive linear range. • This new production of an electrochemical biosensor serves as a straightforward and rapid instrument for identifying Alexandrium minutum DNA in water samples tainted with this detrimental algae. Alexandrium species, including Alexandrium minutum (A. minutum) , are capable of producing paralytic shellfish toxins, which frequently adversely affect the aquaculture and fishing industries. Since it's critical, it needs to be precisely detected. This study addresses the development of an electrochemical DNA biosensor for detecting toxic microalga A. minutum gene sequence based on anthraquinone-2-sulfonic acid derivative (AQMS) as the redox DNA hybridisation indicator. DNA binding studies using UV–Vis and molecular docking were performed, confirming the intercalation behaviour. The binding constant (K b) of such interaction was 4.5 × 105 M−1 with the hyperchromicities shown are 13 % and 18 %, and the relative binding energies of the docked AQMS towards DNA was − 8.3 kcal mol−1. The RMSD value for AQMS was 0.2 Å, underscoring a remarkably close alignment and similarity with the redocked structure. The aminated DNA probe was then immobilised onto the screen-printed carbon electrode (SPCE) containing polyacrylic microspheres and gold nanoparticles (AuNPs). An excellent linear relationship of the response to DNA concentrations was obtained from 1 × 10−15 M to 1 × 10−5 M (R2 = 0.9908) with a limit detection (LOD) at 6.91 × 10−14 M. This lower detection limit is a significant improvement over several other electrochemical biosensors reported so far for A. minutum determinations. Selectivity experiments demonstrated that this new voltammetric DNA biosensor could distinguish between A. minutum target and non-target DNA and can regenerate after use for up to two cycles. This DNA biosensor has demonstrated its ability to early detect toxic microalgae by effectively differentiating among various non-target dinoflagellate species. Furthermore, the biosensor has been shown to successfully identify A. minutum in water samples from a river in Tumpat, Kelantan, with results comparable to standard polymerase chain reaction (PCR). [ABSTRACT FROM AUTHOR]

A novel electrochemical DNA biosensor for ultrasensitive and selective quantitation of Escherichia coli DNA based on aminated hollow silica spheres (HSiSs) has been successfully developed. The HSiSs were synthesized with facile sonication and heating techniques. The HSiSs have an inner and an outer surface for DNA immobilization sites after they have been functionalized with 3-aminopropyltriethoxysilane. From field emission scanning electron microscopy images, the presence of pores was confirmed in the functionalized HSiSs. Furthermore, Brunauer-Emmett-Teller (BET) analysis indicated that the HSiSs have four times more surface area than silica spheres that have no pores. These aminated HSiSs were deposited onto a screen-printed carbon paste electrode containing a layer of gold nanoparticles (AuNPs) to form a AuNP/HSiS hybrid sensor membrane matrix. Aminated DNA probes were grafted onto the AuNP/HSiS-modified screen-printed electrode via imine covalent bonds with use of glutaraldehyde cross-linker. The DNA hybridization reaction was studied by differential pulse voltammetry using an anthraquinone redox intercalator as the electroactive DNA hybridization label. The DNA biosensor demonstrated a linear response over a wide target sequence concentration range of 1.0×10-12-1.0×10-2 μM, with a low detection limit of 8.17×10-14 μM (R2 = 0.99). The improved performance of the DNA biosensor appeared to be due to the hollow structure and rough surface morphology of the hollow silica particles, which greatly increased the total binding surface area for high DNA loading capacity. The HSiSs also facilitated molecule diffusion through the silica hollow structure, and substantially improved the overall DNA hybridization assay.Step-by-step DNA biosensor fabrication based on aminated hollow silica spheres [ABSTRACT FROM AUTHOR]