Histamine is one of the important biomarkers for food spoilage in the food sectors. In the present study, a rapid and simple analytical tool has been developed to detect histamine as an indirect strategy to monitor food freshness level. Optical histamine sensor with carboxyl-substituted Schiff base zinc(II) complex with hydroxypropoxy side chain deposited onto titanium dioxide nanoparticles was fabricated and was found to respond successfully to histamine. The Schiff base zinc(II) complex-histamine binding generated an enhancement of the fluorescent signal. Under the optimal reaction condition, the developed sensor can detect down to 2.53 × 10-10 M in the range of between 1.0 × 10-9 and 1.0 × 10-5 M (R2 = 0.9868). Selectivity performance of the sensor towards histamine over other amines was confirmed. The sensor also displayed good reproducibility performances with low relative standard deviation values (1.45%-4.95%). Shelf-life studies suggested that the developed sensor remains stable after 60 days in histamine detection. More importantly, the proposed sensor has been successfully applied to determine histamine in salmon fillet with good recoveries. This strategy has a promising potential in the food quality assurance sectors, especially in controlling the food safety for healthy consumption among consumers.
A sensitive and selective optical DNA biosensor was developed for dengue virus detection based on novel square-planar piperidine side chain-functionalized N,N'-bis-4-(hydroxysalicylidene)-phenylenediamine-nickel(II), which was able to intercalate via nucleobase stacking within DNA and be functionalized as an optical DNA hybridization marker. 3-Aminopropyltriethoxysilane (APTS)-modified porous silica nanospheres (PSiNs), was synthesized with a facile mini-emulsion method to act as a high capacity DNA carrier matrix. The Schiff base salphen complexes-labelled probe to target nucleic acid on the PSiNs renders a colour change of the DNA biosensor to a yellow background colour, which could be quantified via a reflectance transduction method. The reflectometric DNA biosensor demonstrated a wide linear response range to target DNA over the concentration range of 1.0 × 10-16-1.0 × 10-10 M (R² = 0.9879) with an ultralow limit of detection (LOD) at 0.2 aM. The optical DNA biosensor response was stable and maintainable at 92.8% of its initial response for up to seven days of storage duration with a response time of 90 min. The reflectance DNA biosensor obtained promising recovery values of close to 100% for the detection of spiked synthetic dengue virus serotypes 2 (DENV-2) DNA concentration in non-invasive human samples, indicating the high accuracy of the proposed DNA analytical method for early diagnosis of all potential infectious diseases or pathological genotypes.
The platinum(II) salphen complex N,N'-Bis-4-(hydroxysalicylidene)-phenylenediamine-platinum(II); (1) and its two derivatives containing hydroxyl functionalized side chains N,N'-bis-[4-[[1-(2-hydroxyethoxy)] salicylidene] phenylenediamine-platinum(II); (2) and N,N'-bis-[4-[[1-(3-hydroxypropoxy)] salicylidene] phenylenediamine-platinum(II); (3) were synthesized and characterized. The structures of the complexes were confirmed by 1H and 13C NMR spectroscopy, FTIR, ESI-MS and CHN elemental analyses. The effects of the hydroxyl substituent on the spectral properties and the DNA binding behaviors of the Pt(II) complexes were explored. The binding mode and interactions of these complexes with duplex DNA (calf thymus DNA and porcine DNA) and also single-stranded DNA were studied by UV-Vis and emission DNA titration. The complexes interact with DNA by intercalation binding mode with the binding constants in the order of magnitude (Kb = 104 M-1, CT-DNA) and (Kb = 105 M-1, porcine DNA). The intercalation of the complex in the DNA structure was proposed to happen by π-π stacking due to its square-planar geometry and aromatic rings structure. The phosphorescence emission spectral characteristics of Pt(II) complexes when interacted with DNA have been studied. Also, the application of the chosen hydroxypropoxy side chains complex (3) as an optical DNA biosensor, specifically for porcine DNA was investigated. These findings will be valuable for the potential use of the platinum(II) salphen complex as an optical DNA biosensor for the detection of porcine DNA in food products.
Biogenic amines have attracted interest among researchers because of their importance as biomarkers in determining the quality of food freshness in the food industry. A rapid and simple technique that is able to detect biogenic amines is needed. In this work, a new optical sensing material for one of the biogenic amines, histamine, based on a new zinc(II) salphen complex was developed. The binding of zinc(II) complexes without an electron-withdrawing group (complex 1) and with electron-withdrawing groups (F, complex 2; Cl, complex 3) to histamine resulted in enhancement of fluorescence. All complexes exhibited high affinity for histamine [binding constant of (7.14 ± 0.80) × 104, (3.33 ± 0.03) × 105, and (2.35 ± 0.14) × 105 M-1, respectively]. Complex 2 was chosen as the sensing material for further development of an optical sensor for biogenic amines in the following step since it displayed enhanced optical properties in comparison with complexes 1 and 3. The optical sensor for biogenic amines used silica microparticles as the immobilisation support and histamine as the analyte. The optical sensor had a limit of detection for histamine of 4.4 × 10-12 M, with a linear working range between 1.0 × 10-11 and 1.0 × 10-6 M (R2 = 0.9844). The sensor showed good reproducibility, with a low relative standard deviation (5.5 %). In addition, the sensor exhibited good selectivity towards histamine and cadaverine over other amines, such as 1,2-phenylenediamine, triethylamine, and trimethylamine. Recovery and real sample studies suggested that complex 2 could be a promising biogenic amine optical sensing material that can be applied in the food industry, especially in controlling the safety of food for it to remain fresh and healthy for consumption.
An optical aptasensor-based sensing platform for rapid insulin detection was fabricated. Aminated porous silica microparticles (PSiMPs) were synthesized via a facile mini-emulsion method to provide large surface area for covalent immobilization of insulin-binding DNA aptamer (IGA3) by glutaraldehyde cross-linking protocol. A Nickel-salphen type complex with piperidine side chain [Ni(II)-SP] was synthesized with a simple one-pot reaction, and functionalized as an optical label due to strong π-π interaction between aromatic carbons of G-quadruplex DNA aptamer and planar aromatic groups of Ni(II)-SP to form the immobilized IGA3-Ni(II)-SP complex, i.e. the dye-labeled aptamer, thereby bringing yellow colouration to the immobilized G-quartet plane. Optical characterization of aptasensor towards insulin binding was carried out with a fiber optic reflectance spectrophotometer. The maximum reflectance intensity of the immobilized IGA3-Ni(II)-SP complex at 656 nm decreased upon binding with insulin as aptasensor changed to brownish orange colouration in the background. This allows optical detection of insulin as the colour change of aptasensor is dependent on the insulin concentration. The linear detection range of the aptasensor is obtained from 10 to 50 μIU mL-1 (R2 = 0.9757), which conformed to the normal fasting insulin levels in human with a limit of detection (LOD) at 3.71 μIU mL-1. The aptasensor showed fast response time of 40 min and long shelf life stability of >3 weeks. Insulin detection using healthy human serums with informed consent provided by participants suggests the DNA aptamer biosensor was in good agreement with ELISA standard method using BIOMATIK Human INS (Insulin) ELISA Kit.
A novel label-free electrochemical DNA biosensor was constructed for the determination of Escherichia coli bacteria in environmental water samples. The aminated DNA probe was immobilized onto hollow silica microspheres (HSMs) functionalized with 3-aminopropyltriethoxysilane and deposited onto a screen-printed electrode (SPE) carbon paste with supported gold nanoparticles (AuNPs). The biosensor was optimized for higher specificity and sensitivity. The label-free E. coli DNA biosensor exhibited a dynamic linear response range of 1 × 10-10 µM to 1 × 10-5 µM (R2 = 0.982), with a limit of detection at 1.95 × 10-15 µM, without a redox mediator. The sensitivity of the developed DNA biosensor was comparable to the non-complementary and single-base mismatched DNA. The DNA biosensor demonstrated a stable response up to 21 days of storage at 4 ℃ and pH 7. The DNA biosensor response was regenerable over three successive regeneration and rehybridization cycles.