A Novel Colorimetric Nano Aptasensor for Ultrasensitive Detection of Aflatoxin B1 Based on the Exonuclease III-Assisted Signal Amplification Approach

The detection of aflatoxin B1 (AFB1) has recently garnered much attention on the issue of food safety. In this study, a novel and sensitive aptasensor towards AFB1 is proposed using an Exonuclease III (Exo III)-integrated signal amplification strategy. This reported sensing strategy is regulated by aptamer-functionalized nanobeads that can target AFB1; furthermore, complementary DNA (cDNA) strands can lock the immobilized aptamer strands, preventing the signal amplification function of Exo III in the absence of AFB1. The presence of AFB1 triggers the displacement of cDNA, which will then activate the Exo III-integrated signal amplification procedure, resulting in the generation of a guanine (G)-rich sequence to form a G-4/hemin DNAzyme, which can catalyze the substrate of ABTS to produce a green color. Using this method, a practical detection limit of 0.0032 ng/mL and a dynamic range of detection from 0.0032 to 50 ng/mL were obtained. Additionally, the practical application of the established sensing method for AFB1 in complex matrices was demonstrated through recovery experiments. The recovery rate and relative standard deviations (RSD) in three kinds of cereal samples ranged from 93.83% to 111.58%, and 0.82% to 7.20%, respectively, which were comparable with or better than previously reported methods.

DO INDONESIAN GOVERNMENT DEPLOY RELIABLE AMMUNITION FOR COVID-19 MASS TEST? A COMPARISON OF REAL-TIME PCR KITS

Objective: This study aimed to compare the level of reliability of three commercial real-time PCR kits in determining clinical samples. Methods: A total of 40 swabs samples which were previously tested positive, were re-test using the BioCov-19 RT-PCR kit, Sansure coronavirus disease 19 (COVID-19) nucleic acid diagnostic kit, and Kogen PowerCheck with Thermocycler (Roche). The amplification procedure is carried out based on the manual for each kit. Results: Sansure COVID-19 nucleic acid diagnostic was able to detect 40 samples with positive severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) results detected in both genes, while the PowerChek™ 2019-nCoV real-time PCR kit able to detect 35 samples showed that SARS-COV-II was detected in both genes, and the BioCoV-19 RT-PCR Kit brand kit able to detect 34 samples showed positive SARS-COV-2 results in both genes. Conclusion: The three commercial kits show great ability detection, so that they can be used to detect the presence of SARS-COV-II in clinical samples, and also in mass screening.

Enhanced Colorimetric Signal for Accurate Signal Detection in Paper-Based Biosensors

Paper-based colorimetric biosensors combine the use of paper with colorimetric signal detection. However, they usually demonstrate lower sensitivities because a signal amplification procedure has not been used. Stopping the reaction of colorimetric signal generation is often used in lab-based assays in order to amplify and stabilize the colorimetric signal for detection. In this study, the generation of a stopped colorimetric signal was examined for accurate and enhanced signal detection in paper-based biosensors. The colorimetric reaction in biosensors is usually based on the interaction between the enzyme horseradish peroxidase (HRP) and a selected chromogenic substrate. The two most commonly used HRP substrates, 3,3’,5,5’-tetramethylbenzidine (TMB) and 2’-azinobis (3-ethylbenzothiazoline-6-sulfonic-acid) (ABTS), were compared in terms of their ability to generate a stopped colorimetric signal on membrane. The stopped colorimetric signal was visible for TMB but not for ABTS. Moreover, the generation of stopped colorimetric signal was dependent on the presence of polyvinylidene-difluoride (PVDF) membrane as the separation layer. With PVDF the colorimetric signal (color intensity) was higher (TMB: 126 ± 6 and ABTS: 121 ± 9) in comparison to without PVDF (TMB: 110 ± 2 and ABTS: 102 ± 4). The TMB stopped colorimetric signal demonstrated a more stable signal detection with lower standard deviation values. To conclude, a stopped colorimetric signal can be generated in paper-based biosensors for enhanced and accurate signal detection.

Sample Biological Material Operating Procedure for the method of molecular-biological techniques (PCR diagnostics)

Review describes a method of diagnostics with the use of the polymerase chain reaction (PCR diagnostics) of infections in patients in modern obstetric-gynecological practice. Particular attention is paid to urogenital tract pathogens to be diagnosed by the method of nucleic acid amplification. There are described the preparation for the study, purposes, the technology of amplification procedure. There is shown the difference in the detection of the DNA and RNA pathogen. The presented photographs show in detail all the stages of obtaining scrapings from the urogenital tract.

Development of a Loop-Mediated Isothermal Amplification Procedure as a Sensitive and Rapid Method for Detection of ‘Candidatus Liberibacter solanacearum’ in Potatoes and Psyllids

This study reports the development of a loop-mediated isothermal amplification procedure (LAMP) for polymerase chain reaction (PCR)-based detection of ‘Candidatus Liberibacter solanacearum’, the bacterial causal agent of potato zebra chip (ZC) disease. The 16S rDNA gene of ‘Ca. Liberibacter solanacearum’ was used to design a set of six primers for LAMP PCR detection of the bacterial pathogen in potato plants and the psyllid vector. The advantage of the LAMP method is that it does not require a thermocycler for amplification or agarose gel electrophoresis for resolution. Positive LAMP results can be visualized directly as a precipitate. The LAMP strategy reported here reliably detected ‘Ca. Liberibacter solanacearum’ and the closely related species ‘Ca. Liberibacter asiaticus’, the causative agent of huanglongbing disease of citrus, in plant DNA extracts. Although not as sensitive as quantitative real-time PCR, LAMP detection was equivalent to conventional PCR in tests of ZC-infected potato plants from the field. Thus, the LAMP method shows strong promise as a reliable, rapid, and cost-effective method of detecting ‘Ca. Liberibacter’ pathogens in psyllids and field-grown potato plants and tubers.