In this paper, a Whole-Bacteria SELEX (WB-SELEX) strategy was adopted to isolate specific aptamers against Shigella sonnei. Real-time PCR amplification and post-SELEX experiment revealed that the selected aptmers possessed a high binding affinity and specificity for S. sonnei. Of the 21 aptamers tested, the C(t) values of the SS-3 and SS-4 aptamers (Ct = 13.89 and Ct = 12.23, respectively) had the lowest value compared to other aptamer candidates. The SS-3 and SS-4 aptamers also displayed a binding affinity (K_D) of 39.32 ± 5.02 nM and 15.89 ± 1.77 nM, respectively. An aptamer-based fluorescent biosensor assay was designed to detect and discriminate S. sonnei cells using a sandwich complex pair of SS-3 and SS-4. The detection of S. sonnei by the aptamer based fluorescent biosensor platform consisted of three elements: (1) 5’amine-SS-4 modification in a 96-well type microtiter plate surface (N-oxysuccinimide, NOS) as capture probes; (2) the incubation with S. sonnei and test microbes in functionalized 96 assay wells in parallel; (3) the readout of fluorescent activity using a Cy5-labeled SS-3 aptamer as the detector. Our platform showed a significant ability to detect and discriminate S. sonnei from other enteric species such as E. coli, Salmonella typhimurium and other Shigella species (S. flexneri, S. boydii). In this study, we demonstrated the feasibility of an aptamer sensor platform to detect S. sonnei in a variety of foods and pave the way for its use in diagnosing shigellosis through multiple, portable designs.

We validated a single-stranded, DNA aptamer-based, diagnostic method capable of detecting Lipocalin-2 (LCN2), a biomarker from clinically relevant hepatocellular carcinoma (HCC) patient serum, in the sandwich assay format. Nine aptamers (LCN2_apta1 to LCN2_apta9) for LCN2 were screened with SELEX processes and a sandwich pair (LCN2_apta2 and LCN2_apta4) was finally chosen using surface plasmon resonance (SPR) and dot blotting analysis. The result of the proposed aptamer sandwich construction shows that LCN2 was sensitively detected in the concentration range of 2.5–500 ng mL⁻¹ with a limit of detection of 0.6 ng mL⁻¹. Quantitative measurement tests in HCC patients were run on straight serum and were compared with the performance of the conventional antibody-based ELISA kit. The aptamer sandwich assay demonstrated an excellent dynamic range for LCN2 at clinically relevant serum levels, covering sub-nanogram per mL concentrations. The new approach offers a simple and robust method for detecting serum biomarkers that have low and moderate abundance. It consists of functionalization, hybridization and signal read-out and no dilution is required. The results of the study demonstrate the capability of the aptamer sandwich assay platform for diagnosing HCC and its potential applicability to the point-of-care testing (POCT) system.

The objective of this study was to determine toxicities of four parabens (methyl paraben, MP; ethyl paraben, EP; n-propyl paraben, PP; and n-butyl paraben; BP) and their mixtures to two aquatic microorganisms, Daphnia magna and Aliivibrio fischeri. Parabens are one of the widely used preservatives for personal care products, such as cosmetics, pharmaceuticals and food also. First, each paraben was treated to D. magna to measure the toxicity levels as LC20 and LC50. The results showed their value of MP (25.2 mg/L, 73.4 mg/L), EP (18.4 mg/L, 43.7 mg/L), PP (10.4 mg/L, 21.1 mg/L) and BP (3.3 mg/L, 11.2 mg/L). Then, each of the parabens was treated to A. fischeri and calculated their EC20 and EC50 by bioluminescence inhibition test. The results showed the values of MP (2.93 mg/L, 16.8 mg/L), EP (1.18 mg/L, 6.74 mg/L), PP (0.51 mg/L, 5.85 mg/L) and BP (0.21 mg/L, 2.34 mg/L). These four parabens belong to the group classified as being 'harmful to aquatic organisms' (above 10 mg/L, below 100 mg/L). After measuring the toxicity, EC20 values of two or more parabens were tested in order to investigate their toxicity. A total of ten combinations of four parabens were tested. As a result, the bioluminescence inhibition test of A. fischeri showed that the toxicity of mixture parabens was stronger than that of a single compound and combinations of three parabens showed the highest bioluminescence inhibition. These results showed that independent toxicity of paraben was maintained. Therefore, it can be predictable that the toxicity of paraben is getting stronger by the addition of other parabens.