Colorimetric Test Research Articles

Characterization and Applicability of a Bone Spheroid Model for the Evaluation of Cytocompatibility of Bone Substitutes

In vitro cell-based tests are an important preclinical step for the safety assessment of biomaterials and drugs. Three-dimensional cell culture models (3D) may improve the limitations of the usual 2D models, as they better simulate a physiological environment. This work describes the characterization of a 3D spheroid model of MC3T3-E1 murine preosteoblasts for the testing of bone-substitute materials and investigates its adequacy to some of the most employed cell viability tests. The spheroids presented structural stability for 28 days in culture, with a regular spheroidal aspect, compact surface, and dense inner structure, with high potential for mineralization, but a time-dependent reduction in size. The use of colorimetric tests (MTT, XTT, and NRU) did not achieve satisfactory optical densities and did not correlate with cell density in the 3D model, as the aggregates remain strongly stained even after dye extraction steps. On the other hand, the LDH test achieved appropriate optical density and a high correlation with cell density (r2 = 0.77) and identified a dose–response for a well-known cytotoxic polymer (latex), while no toxicity was identified for biocompatible PLA wires. These results indicate that material testing with 3D bone cell models requires a careful choice of test methods and parameters.

Chemical Composition, Biomolecular Analysis, and Nuclear Magnetic Resonance Spectroscopic Fingerprinting of Posidonia oceanica and Ascophyllum nodosum Extracts.

A detailed analysis of the elemental and molecular composition of Posidonia oceanica (PO) and Ascophyllum nodosum (AN) is presented. In particular, an in-depth study of the molecular identification via NMR spectroscopy of aqueous and organic extracts of PO and AN was carried out, exploiting 2D COSY and pseudo-2D DOSY data to aid in the assignment of peaks in complex 1D proton NMR spectra. Many metabolites were identified, such as carbohydrates, amino acids, organic acids, fatty acids, and polyphenols, with NMR complementing the characterization of the two species by standard elemental analysis, HPLC analysis, and colorimetric testing. For PO, different parts of the live plant (roots, rhizomes, and leaves) were analysed, as well as the residues of the dead plant which typically deposit along the coasts. The combination of the various studies made it possible to recognize bioactive compounds naturally present in the two plant species and, in particular, in the PO residues, opening the door for their possible recycling and use in, for example, fertilizer. Furthermore, NMR is proven to be a powerful tool for the metabolomic study of plant species as it allows for the direct identification of specific biomarkers as well as providing a molecular fingerprint of the plant variety.

Plasmon-Mediated Oxidase-like Activity on Ag@ZnS Heterostructured Hollow Nanowires for Rapid Visual Detection of Nitrite.

Rational design of fast and sensitive determination of nitrite (NO2-) from a complicated actual sample overtakes a crucial role in constructing a high-efficiency sensing platform. Herein, a visual NO2- sensing platform with outstanding selectivity, sensitivity, and stability based on a surface plasmon resonance (SPR)-enhanced oxidase-like activity has been proposed. Benefiting from the intrinsic photocatalytic activity and limited light penetration of ZnS, the oxidase-like activity based on ZnS decorated on Ag nanowires (Ag@ZnS) is determined. It is demonstrated that the electrons are generated efficiently on the surface of ZnS and then transferred into the hot electrons of Ag with the help of localized SPR excitation, thus greatly oxidating the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to produce dark blue oxidized TMB (oxTMB). When nitrite is added into the reaction system, the oxTMB will selectively react with NO2- to generate diazotized oxTMB, leading to a visual color change from dark blue to light green and subsequently to dark yellow. Owing to the specific recognition between nitrite and oxTMB, the recovery of catalytic activity induced an enhanced colorimetric test with a wider linear range for NO2- determination, an ultralow detection limit of 0.1 μM, excellent selectivity, and practicability for application in real samples. This plasmon-enhanced oxidase-like activity not only provides a smart approach to realize a colorimetric assay with high sensitivity and simplicity but also modulates oxidase-like activities.

A rapid colorimetric dual sensor for the detection of mercury and lead ions in water using cysteine capped silver nanoparticles

Thiol groups containing amino acids like cystine and l-cysteine help in the chelation of poisonous heavy metals in biological systems therein making them eliminated easily in urine. Based on this phenomenon, cysteine-coated silver nanoparticles could be helpful as potential label-free sensors systems for detecting heavy metals. In this study, the benefit of using silver nanoparticles with cysteine capping (Cys-AgNPs) for colorimetric detection of individual and simultaneous sensing of Lead(Pb2+) and Mercury( Hg2+) in water samples was reported. Cys-AgNPs were characterized using spectroscopy, microscopy, X-ray diffractometer analysis and the photophysical properties of the particles towards Hg2+ and Pb2+ ions were investigated through absorption spectroscopy and colorimetric tests. Upon exposure of Hg2+ ions to Cys-AgNPs, a hypsochromic shift in the surface plasmon resonance (SPR) band with decreased intensity was detected. In contrast, it was a bathochromic shift with an increase in absorbance intensity observed with Pb2+ ions. Cys-AgNPs are highly sensitive toward Hg2+ and Pb2+ ions individually with clear color changes in the solution visible to the naked eye. The limit of detection (LOD) was found to be 45.39 × 10−9 M (for Hg2+ ions) and 49.39 × 10−9 M (for Pb2+ ions). Furthermore, dual ion sensing ability was also assessed by Cys-AgNPs by varying Hg2+ and Pb2+ ions individually in water samples. The LOD for constant Hg2+ and varying Pb2+ was found to be 43 × 10−9 M while it is 37.95 × 10−9 M for constant Pb2+ and varying Hg2+. These results determine that the Cys-AgNPs system has potential application as a colorimetric sensor for the detection of individual or mixed Hg2+ and Pb2+ ions in water samples quickly.

Using colorimetric spot test and digital imaging-based technique for volatile acidity determination in cachaça with the aid of a smartphone

The present study reports the development and application of a novel method for the colorimetric determination of volatile acidity in cachaça using digital image. Cachaça is the most widely consumed beverage in Brazil and the development of efficient techniques for the determination of volatile acidity in this beverage is essentially important because this parameter directly reflects on the flavor and aroma of the drink. The method employed was digital image-based (DIB); this method involves the use of methyl orange as an indicator and the analysis of images captured and processed by a smartphone with a free application. A simple pretreatment of the samples employing a steam-dragging distillation for the extraction of volatile acids was performed before DIB analysis. The calibration curve related to anhydrous alcohol was found to be linear in the range of 25 to 275 mg/100 mL with an adjusted-R2 = 0.9912 and limit of detection of 6.70 mg/100 mL based on acetic acid content. The recovery assays conducted yielded recoveries ranging from 89.5 and 112 %. The technique proposed in this study is an easy, inexpensive and rapid tool for the quality control of cachaça, especially for small producers of the beverage who have limited financial resources. Moreover, this method is applicable to in situ analysis allowing to measure this parameter along the cachaça are produced being useful to monitor the volatile acidity.

Analytical performance and “receiver operating characteristic curve” analysis of resazurin assay for seed-viability estimation in flax

ABSTRACT Germination capacity is an important parameter of seed viability. The direct germination test destroys the seed. Viability evaluation by nondestructive tests allows the saving of seeds for storage and future use. However, predictive values of most nondestructive tests have not been adequately determined. This study investigated performance parameters and optimized assay conditions for a nondestructive colorimetric resazurin seed-viability test of flax seeds (Linum usitatissimum L.). In this study, 800 seeds were tested by resazurin test before germination. Optimization of resazurin test conditions and cutoff value was determined via a “receiver operating characteristic curve” analysis. We found that the optimal incubation time was 2 h. We proposed to measure sample absorption at 595 nm for better seed-viability estimation by resazurin test due to spectral properties of dye. We improved sensitivity of the resazurin test by using measurements adjusted to blank absorption at 595 nm (sensitivity 91%) or to sample absorption at 490 nm (sensitivity 95% versus 81% before corrections). The resazurin test reliably predicted germinable seeds in 72–73% cases and ungerminable seeds in 92–95% cases, with a sensitivity of 91–95% and a specificity of 71–74%. Therefore, the easy and low-cost resazurin test exhibited analytical performance similar to more expensive instrumental tests and can be suitable for nondestructive seed-viability estimation.

Screening of lactic acid bacteria strains isolated from Iranian traditional dairy products for GABA production and optimization by response surface methodology

A total of 50 lactic acid bacteria (LAB) isolates from Iranian traditional dairy products (Motal and Lighvan cheeses, and artisanal yogurt) were screened for gamma-aminobutyric acid (GABA) production. Firstly, a rapid colorimetric test was performed to evaluate the glutamate decarboxylase (GAD) activity among the LAB isolates examined. Thin layer chromatography (TLC) was then performed on selected strains to identify isolates with high/moderate GABA producing capacity, and a GABase micro-titer plate assay was employed to quantify GABA. Finally, two Lactococcus (Lac.) lactis strains were selected for GABA production optimization via Response Surface Methodology (RSM) following Central Composite Design (CCD). Forty-one out of the 50 isolates showed GAD activity according to the colorimetric assay. Eight isolates displayed strong GAD activity, while nine showed no activity; low to moderate GAD activity was scored for all other isolates. GABA production was confirmed by TLC in all isolates with high GAD activity and in four selected among isoaltes with moderate activity. Among the Lactococcus strains tested, Lac. lactis 311 and Lac. lactis 491 were the strongest GABA producers with amounts of 3.3 and 1.26 mM, respectively. These two strains were subjected to GABA production optimization applying RSM and CCD on three key variables: Monosodium glutamate concentration (MSG) (between 25 and 150 mM), incubation temperature (between 25 and 37 °C), and pH (between 4.0 and 5.0). Optimal conditions for GABA production by Lac. lactis 311 and Lac. lactis 491 of temperature, pH and MSG concentration were, respectively, 35.4 and 30 °C, pH 4.5 and 4.6, and MSG concentration of 89 and 147.4 mM, respectively. Under the above conditions, the amount of GABA produced by Lac. lactis 311 and Lac. lactis 491 was 0.395 and 0.179 mg/mL, respectively. These strains and the optimal culture conditions determined in this study could be used for the biotechnological production of GABA or applied in food fermentations for the development of naturally GABA-enriched foods.

Microfluidic paper-based colorimetric quantification of malondialdehyde using silver nanoprism toward on-site biomedical analysis: a new platform for the chemical sensing and biosensing of oxidative stress.

Malondialdehyde (MDA) is a critical product of polyunsaturated adipose acid peroxidation and represents a common biomarker of oxidative stress. The effect of different MDA concentrations on human biofluids reflects pathological changes, which has been seen in diverse types of sickness, such as leukemia, diabetes, cancer, cardiovascular disease, and age-related macular degeneration and liver disease. In this study, different types of silver nanoparticles, including silver nanoprism (AgNPrs), silver nanowires (AgNWs), and silver nanospheres (AgNSs), were synthesized and used for the chemosensing of MDA by colorimetric and spectrophotometric methods. Colorimetric tests were performed to identify malondialdehyde in the solution as well as the one-droplet-based microfluidic paper substrate as a miniaturization device for the monitoring of analytes in human real samples. The analytical quantification of the MDA was done using the UV-Vis method. Also, the utilization of the designed chemosensor for the analysis of MDA in real sample was evaluated in human urine samples. Using the spectrophotometric method, MDA was deformed in the linear range of 0.01192 to 1.192 mM with a low limit of quantification of 0.12 μM. Essential significant features of this study include the first application of AgNPrs with high stability and great optical properties without any reagent as an optical sensing probe of MDA and optimized OD-μPCD toward on-site and on-demand MDA screening in real samples diagnosis and the innovative time/color semi-analytical recognition strategy. Moreover, the prepared OD-μPCD decorated by AgNPrs could be a prized candidate for commercialization due to the benefits of the low-cost materials used, like paper and paraffin, and portability. This innovative process led to uniform hydrophilic micro-channels on the surface of cellulose, without the use of a UV lamp, clean room, and organic solvents. This report could be a pioneering work, inspiring simple and effective on-site semi-analytical recognition devices for harmful substances or illegal drugs, which simply consist of a piece of lightweight paper and one drop of the required reagent.

High-precision, low-complexity, high-resolution microscopy-based cell sorting.

Continuous flow cell sorting based on image analysis is a powerful concept that exploits spatially-resolved features in cells, such as subcellular protein localisation or cell and organelle morphology, to isolate highly specialised cell types that were previously inaccessible to biomedical research, biotechnology, and medicine. Recently, sorting protocols have been proposed that achieve impressive throughput by combining ultra-high flow rates with sophisticated imaging and data processing protocols. However, moderate image quality and high complex experimental setups still prevent the full potential of image-activated cell sorting from being a general-purpose tool. Here, we present a new low-complexity microfluidic approach based on high numerical aperture wide-field microscopy and precise dielectrophoretic cell handling. It provides high-quality images with unprecedented resolution in image-activated cell sorting (i.e., 216 nm). In addition, it also allows long image processing times of several hundred milliseconds for thorough image analysis, while ensuring reliable and low-loss cell processing. Using our approach, we sorted live T cells based on subcellular localisation of fluorescence signals and demonstrated that purities above 80% are possible while targeting maximum yields and sample volume throughputs in the range of μl min-1. We were able to recover 85% of the target cells analysed. Finally, we ensure and quantify the full vitality of the sorted cells cultivating the cells for a period of time and through colorimetric viability tests.

Validation of a rapid test to dose SO<sub>2</sub> in vinegar

<abstract> <p>Sulfur dioxide is generally used in wine and vinegar production. It is employed to decrease the bacteria' growth, improve the wines' aroma (since it supports the extraction of polyphenols during maceration), protect the wines from chemical oxidation and the musts from chemical and enzymatic oxidation (blocking free radicals and oxidase enzymes such as tyrosinase and laccase). The composition and storage conditions (i.e., pH, temperature, and alcohol levels) affect oenological results. In various countries, competent authorities have imposed legal limits since it can have toxic effects on humans. It is crucial to dose SO<sub>2</sub> levels to allow vinegar production and compliance with legal limits. The iodometric titration named "Ripper test" is the legal method used to dose it in vinegar. In this work, an automatized colorimetric test was validated using the international guidelines ISO/IEC (2017) to allow its use instead of the Ripper test. The test reliability was verified on white, red, and balsamic vinegar with low or high SO<sub>2</sub> content. The automatized test showed linearity, precision, and reproducibility similar to the Ripper test, but the accuracy parameter was not respected for the vinegar with a low concentration of SO<sub>2</sub>. Therefore, the automatized colorimetric test can be helpful to dose SO<sub>2</sub> in vinegar with high concentrations of SO<sub>2</sub>.</p> </abstract>

In vitro evaluation of methanol extracts of edible fungi Pleurotus ostreatus and Lentinula edodes against Rhyssomatus nigerrimus Fahraeus.

The study aimed to evaluate the insecticidal activity of extracts of edible mushrooms Pleurotus ostreatus and Lentinula edodes against Rhyssomatus nigerrimus. Methanol:water extracts (70:30) of P. ostreatus and L. edodes were made and evaluated in two in vitro tests (exposure and immersion toxic effect) against R. nigerrimus. Subsequently, the toxicity test of the extracts against Artemia salina was evaluated. These extracts were subjected to colorimetric tests and gas chromatography-mass spectrometry. The results showed a mortality effect against R. nigerrimus of 50% for the P. ostreatus 2 extracts at a concentration of 20% in the immersion test. Likewise, in the toxic effect test, 90% mortality was observed after five days of exposure to a concentration of 10%. On the other hand, for the toxicity test, the extract that showed the values with the highest mortality against A. salina was P. ostreatus, starting with 80% mortality at 100μg/mL. The functional groups present in the extracts were saponins, coumarins, and alkaloids. Furthermore, the presence of more than 7 compounds in the mushroom extracts evaluated is reported. This study demonstrates the insecticidal activity of P. ostreatus and L. edodes fungal extracts and indicates the importance of using different in vitro tests to elucidate the mechanism of action for future studies.

Computational study of the interaction of the psychoactive amphetamine with 1,2-indanedione and 1,8-diazafluoren-9-one as fingerprinting reagents.

In this study, we used computational methods to investigate the interaction of amphetamine (AMP) with 1,2-indanedione (IND) and 1,8-diazafluoren-9-one (DFO) so as to understand whether AMP can be detected in latent fingerprints using either of these reagents. The results show that the binding energies of AMP with IND and DFO were enhanced by the presence of amino acid from -9.29 to -12.35 kcal mol-1 and -7.98 to -10.65 kcal mol-1, respectively. The physical origins of these interactions could be better understood by symmetry-adapted perturbation theory. The excited state properties of the binding structures with IND demonstrate distinguishable absorption peaks in the UV-vis spectra but zero fluorescence. Furthermore, the UV-vis spectra of the possible reaction products between AMP and the reagents reveal absorption peaks in the visible spectrum. Therefore, we could predict that reaction of AMP with IND would be observable by a reddish colour while with DFO, a colour change to violet is expected. To conclude, the reagents IND and DFO may be used to detect AMP by UV-vis spectroscopy and if their reactions are allowed, the reagents may then act as a potentially rapid, affordable and easy colorimetric test for AMP in latent fingerprints without destruction of the fingerprint sample.

Quantification of pollen viability in Lantana camara by digital holographic microscopy.

Pollen grains represent the male gametes of seed plants and their viability is critical for sexual reproduction in the plant life cycle. Palynology and viability studies have traditionally been used to address a range of botanical, ecological and geological questions, but recent work has revealed the importance of pollen viability in invasion biology as well. Here, we report an efficient visual method for assessing the viability of pollen using digital holographic microscopy (DHM). Imaging data reveal that quantitative phase information provided by the technique can be correlated with viability as indicated by the outcome of the colorimetric test. We successfully test this method on pollen grains of Lantana camara, a well-known alien invasive plant in the tropical world. Our results show that pollen viability may be assessed accurately without the usual staining procedure and suggest potential applications of the DHM methodology to a number of emerging areas in plant science.

Spectrophotometric Analysis of Nitrite in Gunshot Recentness Examinations from Non Toxic Ammunitions: Expanding the Frontiers of Forensic Chemistry

Nitrite ions consist on an important chemical clue related to gunshot examination, concerning to estimation of the time since discharge. Current forensic laboratory methods for nitrite analysis in gunshot residues are well established for investigating conventional ammunition residues. However, the use of these methods to analyze the so-called ecological or “non-toxic” ammunition has been less studied. Here, we have developed a spectrophotometric flow injection analysis method to test nitrite in samples of “non-toxic” ammunition residues. The ammunition used in these experiments was the NTA (non-toxic ammunition) model, .38 caliber, We also investigated the kinetics of nitrite decomposition for this type of ammunition over time. Sulfanilic acid and 1-naphthylethylenediamine in acetic acid were used as colorimetric reagents. The linear dependence of the spectrophotometric signal on the nitrite concentration was as follows: A = 2.07 x 104 µmol-1 L [NO2-] + 6.78 x 10-3 with a correlation coefficient (r) of 0.9994. The standard deviation (SD) of the analytical curve was 3.17 x 10-3 resulting in a limit of detection (LOD) = 0.46 µmol L-1 and a limit of quantification (LOQ) = 1.56 µmol L-1. The proposed instrumental method was more sensitive than conventional colorimetric tests and permitted the detection window to be extended to 32 days while ensuring the safety and reliability required for forensic analysis, in comparison to 7-10 days usually proposed for conventional ammunition. Therefore, the proposed method can be safely employed in forensic laboratories for routine analysis of nitrite ions in GSR samples from ecological or “non-toxic” ammunition.

Evaluation of Total Polyphenol and Flavonoid Contents of Fresh and Dried Pepper (<i>Piper nigrum</i>) from the Ivory Coast

The growing interest in the potential biological activity of polyphenols and flavonoids has highlighted necessity to assess their content in fresh and dried pepper from Ivory Coast. The total polyphenol content was determined using the Folin-Ciocalteu test and the total flavonoid content was also measured spectrophotometrically using the aluminum chloride colorimetric test. The results obtained indicate the total polyphenol levels of fresh and dried peppers are higher in the samples collected in Danane (0.8 ± 0.05 mg GAE/100g) and in Azaguie (0.4 ± 0.08 mg GAE/100g). The lowest concentrations were obtained with fresh and dried pepper samples collected in N’douci (0.22 ± 0.02 mg GAE/100g) and in PK 103 (0.22 ± 0.02 mg GAE/100g). The highest content of total flavonoids was revealed in the locality of PK 103 (1.85 ± 0.62 mg EC/100g) followed by the locality of Maféré (1.37 ± 0.25 mg EC/100g) respectively for black pepper and green pepper. Then, the lowest flavonoid contents were obtained in the dried pepper of Lopou (0.57 ± 0.03 mg EC/100g) and the fresh pepper of PK 103 (0.47 ± 0.03 mg EC/100g). The results obtained highlight the importance of these black spices as promising sources of phenolic compounds and could be used in pharmaceutical treatments and in food.

Isolation and Characterization of Flavonoid Naringenin and Evaluation of Cytotoxic and Biological Efficacy of Water Lilly (Nymphaea mexicana Zucc.).

Despite its limited exploration, Nymphaea mexicana Zucc. can be beneficial if pharmacology, isolation, and biological evaluation are given attention. It is an aquatic species that belongs to the family Nymphaeaceae. The thrust area of the work was the extraction, isolation, and biological evaluation of different extracts of the N. mexicana Zucc. plant. The primary goal of this research was to assess the antimicrobial, antioxidant, and anticancer activities of the extracts and to isolate the target naringenin compound. Comparative FT IR analysis of different extracts of this plant revealed the presence of functional groups of plant secondary metabolites, including polyphenols, flavonoids, terpenoids, esters, amines, glycosides, alkanes, alkaloids, fatty acids, and alcohols. Moderate free radical scavenging potential has been achieved for the various extracts via reducing power and DPPH assays. While cytotoxic activity was evaluated by colorimetric and lactate dehydrogenase cell viability tests on potent cancer cell lines. Lung adenocarcinoma epithelial cells (A-549), and breast cells (MC-7) were treated with MeOH extract. The antimicrobial activity against bacterial strains was evaluated using Gram-positive and -negative cultures, where maximum and minimum inhibition zones were recorded for different strains, including 1.6-25.6 μg/mL for Streptococcus aureus, using the agar well diffusion method. In addition, the anti-inflammatory activity of different extracts of N. mexicana Zucc. was evaluated in a nitrite radical scavenging assay with high concentrations of secondary metabolites, which are important against human pathogens and other diseases.

Albumin-Functionalized Iron Oxide Nanoparticles for Theranostics: Engineering and Long-Term In Situ Imaging.

Magnetic nanosystems (MNSs) consisting of magnetic iron oxide nanoparticles (IONPs) coated by human serum albumin (HSA), commonly used as a component of hybrid nanosystems for theranostics, were engineered and characterized. The HSA coating was obtained by means of adsorption and free radical modification of the protein molecules on the surface of IONPs exhibiting peroxidase-like activity. The generation of hydroxyl radicals in the reaction of IONPs with hydrogen peroxide was proven by the spin trap technique. The methods of dynamic light scattering (DLS) and electron magnetic resonance (EMR) were applied to confirm the stability of the coatings formed on the surface of the IONPs. The synthesized MNSs (d ~35 nm by DLS) were intraarterially administered in tumors implanted to rats in the dose range from 20 to 60 μg per animal and studied in vivo as a contrasting agent for computed tomography. The long-term (within 14 days of the experiment) presence of the MNSs in the tumor vascular bed was detected without immediate or delayed adverse reactions and significant systemic toxic effects during the observation period. The peroxidase-like activity of MNSs was proven by the colorimetric test with o-phenylenediamine (OPD) as a substrate. The potential of the synthesized MNSs to be used for theranostics, particularly, in oncology, was discussed.

Antimicrobial and Antibiofilm Effect of 4,4'-Dihydroxy-azobenzene against Clinically Resistant Staphylococci.

The spread of antibiotic resistance among human and animal pathogens is one of the more significant public health concerns. Moreover, the restrictions on the use of particular antibiotics can limit the options for the treatment of infections in veterinary clinical practice. In this context, searching for alternative antimicrobial substances is crucial nowadays. In this study, 4,4'-dihydroxy-azobenzene (DHAB) was tested for its potential in vitro as an antimicrobial agent against two relevant human and animal pathogens, namely Staphylococcus aureus and Staphylococcus pseudintermedius. The values of minimal inhibitory concentration (MIC) were 64 and 32 mg/L respectively, and they comparable to other azo compounds of probed antimicrobial activity. In addition, the minimal bactericidal concentrations (MCB) were 256 and 64 mg/L. The mechanism by which DHAB produces toxicity in staphylococci has been investigated. DHAB caused membrane damage as revealed by the increase in thiobarbituric acid reactive substances (TBARS) such as malondialdehyde. Furthermore, differential induction of the enzymes peroxidases and superoxide dismutase in S. aureus and S. pseudintermedius suggested their prevalent role in ROS-scavenging due to the oxidative burst induced by this compound in either species. In addition, this substance was able to inhibit the formation of biofilms by both bacteria as observed by colorimetric tests and scanning electron microscopy. In order to assess the relevance of DHAB against clinical strains of MRSA, 10 clinical isolates resistant to either methicillin or daptomycin were assayed; 80% of them gave values of CMI and CMB similar to those of the control S. aureus strain. Finally, cutaneous plasters containing a composite formed by an agar base supplemented with DHAB were designed. These plasters were able to inhibit in vitro the growth of S. aureus and S. pseudintermedius, particularly the later, and this suggests that this substance could be a promising candidate as an alternative to antibiotics in the treatment of animal skin infections, as it has been proven that the toxicity of this substance is very low particularly at a dermal level.

Colorimetric Detection of SARS-CoV-2 Using Plasmonic Biosensors and Smartphones.

Low-cost, instrument-free colorimetric tests were developed to detect SARS-CoV-2 using plasmonic biosensors with Au nanoparticles functionalized with polyclonal antibodies (f-AuNPs). Intense color changes were noted with the naked eye owing to plasmon coupling when f-AuNPs form clusters on the virus, with high sensitivity and a detection limit of 0.28 PFU mL-1 (PFU stands for plaque-forming units) in human saliva. Plasmon coupling was corroborated with computer simulations using the finite-difference time-domain (FDTD) method. The strategies based on preparing plasmonic biosensors with f-AuNPs are robust to permit SARS-CoV-2 detection via dynamic light scattering and UV-vis spectroscopy without interference from other viruses, such as influenza and dengue viruses. The diagnosis was made with a smartphone app after processing the images collected from the smartphone camera, measuring the concentration of SARS-CoV-2. Both image processing and machine learning algorithms were found to provide COVID-19 diagnosis with 100% accuracy for saliva samples. In subsidiary experiments, we observed that the biosensor could be used to detect the virus in river waters without pretreatment. With fast responses and requiring small sample amounts (only 20 μL), these colorimetric tests can be deployed in any location within the point-of-care diagnosis paradigm for epidemiological control.

Concentration measurement of coloured solution using optofluidic approach

In analytical process, measurement of concentration of solution based on colorimetric sensing is normally performed using commercial devices such as colorimeter and spectrophotometer. This approach has several disadvantages such as involving a large volume of reagent and analyte during testing and measurement, unextendible and expensive. Such problem can be solved by replicating its function using a simple optofluidic device with capability of carrying out colorimetric testing with low volume of analyte and reagent. Other benefits of optofluidic devices platforms includes ability to be expanded for automated sensing and mixing for various analytical based reaction. The measurement device works based on the absorbance of absorbance of light, which is related to Beer-Lambert law principles with LED and photodiode as its main optical components. The samples were prepared for concentration ranges between 0.2 to 2.0 M for testing. As a result, it is observed that these concentrations produce a linear voltage calibration curve with correlation coefficient, R2 equal to 0.9944. By using the obtained calibration curve, the final absorbance calculation gives an acceptable linear absorbance concentration with R2 equal to 0.9751 for the tested samples. As a conclusion, these microfluidic platforms not only have a good measurement performance, but also have advantages in terms of its portability and have potential to be implemented for real time application.