Research demonstrates that antioxidants and metal chelators may be of beneficial use in the treatment of neurodegenerative diseases, such as Alzheimer's disease (AD). This study investigated the antioxidant and metal-binding properties of curcumin, capsaicin, and S-allylcysteine, which are major components found in commonly used dietary spice ingredients turmeric, chilli, and garlic, respectively. The DPPH assay demonstrates that these compounds readily scavenge free radicals. These compounds significantly curtail iron- (Fe2+) and quinolinic acid (QA)-induced lipid peroxidation and potently scavenge the superoxide anion generated by 1 mM cyanide in rat brain homogenate. The ferrozine assay was used to measure the extent of Fe2+ chelation, and electrochemistry was employed to measure the Fe3+ binding activity of curcumin, capsaicin, and S-allylcysteine. Both assays demonstrate that these compounds bind Fe2+ and Fe3+ and prevent the redox cycling of iron, suggesting that this may be an additional method through which these agents reduce Fe2+-induced lipid peroxidation. This study demonstrates the antioxidant and metal-binding properties of these spice ingredients, and it is hereby postulate that these compounds have important implications in the prevention or treatment of neurodegenerative diseases such as AD.

Resonant and acoustic wave devices have been researched for several decades for application in the gravimetric sensing of a variety of biological and chemical analytes. These devices operate by coupling the measurand (e.g. analyte adsorption) as a modulation in the physical properties of the acoustic wave (e.g. resonant frequency, acoustic velocity, dissipation) that can then be correlated with the amount of adsorbed analyte. These devices can also be miniaturized with advantages in terms of cost, size and scalability, as well as potential additional features including integration with microfluidics and electronics, scaled sensitivities associated with smaller dimensions and higher operational frequencies, the ability to multiplex detection across arrays of hundreds of devices embedded in a single chip, increased throughput and the ability to interrogate a wider range of modes including within the same device. Additionally, device fabrication is often compatible with semiconductor volume batch manufacturing techniques enabling cost scalability and a high degree of precision and reproducibility in the manufacturing process. Integration with microfluidics handling also enables suitable sample pre-processing/separation/purification/amplification steps that could improve selectivity and the overall signal-to-noise ratio. Three device types are reviewed here: (i) bulk acoustic wave sensors, (ii) surface acoustic wave sensors, and (iii) micro/nano-electromechanical system (MEMS/NEMS) sensors.

The response of an Electrochemical Impedance Spectroscopy (EIS) sensor using DNA aptamers is affected by many factors such as DNA density, charge and conformational changes upon DNA-target binding and buffer conditions. We report here for the first time on the optimisation of an EIS aptamerbased sensor by using Quartz Crystal Microbalance with Dissipation mode (QCM-D). As a case study we employed a DNA aptamer against Prostate Specific Antigen (PSA). PSA detection was achieved by functionalizing the gold sensor surface via thiol chemistry with different ratios of thiolated-DNA aptamer and 6-mercapto-1-hexanol (MCH) used as spacer molecules. PSA binding efficiency can be monitored by measuring QCM-D signals which not only provides information about the mass of PSA bound on the sensor surface but also crucial information about the aptamer conformation and layer hydration.Data generated through QCM-D analysis provided the optimal conditions in terms of aptamer/MCH ratio to maximize the PSA binding. The ratio of 1:200 for DNA aptamer/spacer molecule was found to be optimal for ensuring maximum PSA binding. However, this study showed how a maximum analyte binding does not necessarily correspond to a maximum EIS response, which revealed to be enhanced if a ratio of 1:100 for DNA aptamer/spacer molecule was used. Moreover, by monitoring the QCM-D signal, for the first time a value of the dissociation constant (K d ), equal to 37 nM, was found for the PSA DNA aptamer towards its target. The combination of QCM-D with EIS techniques provide further insight into the effects of mass loading and charge effects that govern the response of an EIS aptasensor, serving as a valuable support for future EIS aptamer-based applications.

BackgroundEarly detection is crucial for the effective treatment of malaria, particularly in those cases infected with Plasmodium falciparum. There is a need for diagnostic devices with the capacity to distinguish P. falciparum from other strains of malaria. Here, aptamers generated against targeted species-specific epitopes of P. falciparum lactate dehydrogenase (rPfLDH) are described.ResultsTwo classes of aptamers bearing high binding affinity and specificity for recombinant P. falciparum lactate dehydrogenase (rPfLDH) and P. falciparum-specific lactate dehydrogenase epitopic oligopeptide (LDHp) were separately generated. Structurally-relevant moieties with particular consensus sequences (GGTAG and GGCG) were found in aptamers reported here and previously published, confirming their importance in recognition of the target, while novel moieties particular to this work (ATTAT and poly-A stretches) were identified. Aptamers with diagnostically-supportive functions were synthesized, prime examples of which are the aptamers designated as LDHp 1, LDHp 11 and rLDH 4 and rLDH 15 in work presented herein. Of the sampled aptamers raised against the recombinant protein, rLDH 4 showed the highest binding to the target rPfLDH in the ELONA assay, with both rLDH 4 and rLDH 15 indicating an ability to discriminate between rPfLDH and rPvLDH. LDHp 11 was generated against a peptide selected as a unique P. falciparum LDH peptide. The aptamer, LDHp 11, like antibodies against the same peptide, only detected rPfLDH and discriminated between rPfLDH and rPvLDH. This was supported by affinity binding experiments where only aptamers generated against a unique species-specific epitope showed an ability to preferentially bind to rPfLDH relative to rPvLDH rather than those generated against the whole recombinant protein. In addition, rLDH 4 and LDHp 11 demonstrated in situ binding to P. falciparum cells during confocal microscopy.ConclusionsThe utilization and application of LDHp 11, an aptamer generated against a unique species-specific epitope of P. falciparum LDH indicated the ability to discriminate between recombinant P. falciparum and Plasmodium vivax LDH. This aptamer holds promise as a biorecognition element in malaria diagnostic devices for the detection, and differentiation, of P. falciparum and P. vivax malaria infections. This study paves the way to explore aptamer generation against targeted species-specific epitopes of other Plasmodium species.

Despite the widespread knowledge of the influence that electrode pretreatments have on electroanalysis, pretreatments of gold electrodes for impedimetric aptasensors remain study-specific. This may be a neglected reason behind the limited consensus in reports focusing on creation and testing of aptasensors. To investigate this, several commonly reported pretreatments were applied to gold electrodes that were subsequently used to fabricate thrombin-specific impedimetric aptasensors, which are widely reported in the literature. Layer-by-layer electrochemical impedance spectroscopy analyses were conducted to determine the effect the pretreatment selection has on impedimetric responses during fabrication and testing of the aptasensor. Pretreatments were evaluated using factors crucial for biosensor deployment: the repeatability of interelectrode measurements and whether biosensors produced statistically significant responses when exposed to 2 μM thrombin. Individual pretreatments were found to impart unique physicochemical properties to electrode surfaces, indicated by variations in measured capacitances (impedimetry) and electrode surface topographies (scanning electron microscopy). Impedimetrically measured resistivity (R total) of electrodes increased during layering of the biosensor across all the investigated pretreatments: from 852 ± 830 Ω (bare electrodes) to 3117 ± 1199 Ω (fabricated aptasensors exposed to thrombin), consistent with prior literature. Crucially, the magnitude and reproducibility of R total values measured during fabrication and testing of the assembled aptasensor were strongly contingent on the pretreatment. Depending on the pretreatment, interelectrode sensor responses exhibited relative standard deviations between 38 and 150%. These findings propose that the choice of gold-surface pretreatment protocols is an overlookedyet crucialfactor to consider when developing analytically valid impedimetric aptasensors.

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A mini-review of the reported biosensor research occurring in South Africa evidences a strong emphasis on electrochemical sensor research, guided by the opportunities this transduction platform holds for low-cost and robust sensing of numerous targets. Many of the reported publications centre on fundamental research into the signal transduction method, using model biorecognition elements, in line with international trends. Other research in this field is spread across several areas including: the application of nanotechnology; the identification and validation of biomarkers; development and testing of biorecognition agents (antibodies and aptamers) and design of electro-catalysts, most notably metallophthalocyanine. Biosensor targets commonly featured were pesticides and metals. Areas  of regional import to sub-Saharan Africa, such as HIV/AIDs and tuberculosis diagnosis, are also apparent in a review of the available literature. Irrespective of the targets, the challenge to the effective deployment of such sensors remains shaped by social and economic realities such that the requirements thereof are for low-cost and universally easy to operate devices for field settings. While it is difficult to disentangle the intertwined roles of national policy, grant funding availability and, certainly, of global trends in shaping areas of emphasis in research, most notable is the strong role that nanotechnology, and to a certain extent biotechnology, plays in research regarding biosensor construction. Stronger emphasis on collaboration between scientists in theoretical modelling, nanomaterials application and or relevant stakeholders in the specific field (e.g., food or health monitoring) and researchers in biosensor design may help evolve focused research efforts towards development and deployment of low-cost biosensors.