Aptamer-based environmental biosensors for small molecule contaminants.

Aptasensors are promising biosensors, which take advantage of using aptamers as a recognition element. The combination of the excellent characteristics of aptamers and the leading detection platform techniques, such as optical, electrochemical with nanomaterial-integrated, or mass-sensitive techniques with high sensitivity and specificity draws a promising view for the application of the aptasensors for the detection of harmful small toxic chemicals and real-time monitoring in the environments. In spite of attraction of aptasensors, application of them is limited to the complex environment due to the facts that how the immobilization of aptamers onto the surface affects the functions of aptamers and their structures for the detection of environmental contaminants are not clearly known. This review examines the most recent update on the selection of aptamers for small molecules, the development and application of aptasensors in the detection of small molecule contaminants in environment. Additionally, their applications to the real samples as environmental monitoring reported in the publications also are reviewed.

A novel reflectance-based aptasensor using gold nanoparticles for the detection of oxytetracycline.

We present a novel reflectance-based colorimetric aptasensor using gold nanoparticles for the detection of oxytetracycline for the first time. It was found that the reflectance-based measurement at two wavelengths (650 and 520 nm) can generate more stable and sensitive signals than absorbance-based sensors to determine the aggregation of AuNPs, even at high AuNP concentrations. One of the most common antibacterial agents, oxytetracycline (OTC), was detected at concentrations as low as 1 nM in both buffer solution and tap water, which was 25-fold more sensitive, compared to the previous absorbance-based colorimetric aptasensors. This reflectance-based colorimetric aptasensor using gold nanoparticles is considered to be a better platform for portable sensing of small molecules using aptamers.

Detection of iprobenfos and edifenphos using a new multi-aptasensor.

The sensitive detection of iprobenfos (IBF) and edifenphos (EDI) was successfully conducted by using a new aptamer-based colorimetric multi-aptasensor. The dissociation constants of this multi-target aptamer to both iprobenfos and edifenphos were found to be 1.67 µM and 38 nM, respectively, according to the isothermal calorimetry assay. The aptamer EIA2 was selective to only IBF and EDI, confirmed by AuNP assays. By using this multi-aptasensor, both pesticides IBF and EDI can be eventually detected in a range from 10 nM to 5 nM, respectively. This multi-aptasensor was successfully implemented in spiked rice samples and the accuracies of this AuNP-based multi-aptasensor were around 80 and 90% in spiked paddy and polished rice samples, respectively. This aptamer EIA2 could be applied not only for the detection of pesticides from real samples in agriculture field as POC, but also can be used as a bioreceptor for other types of aptasensors.

Multiple GO-SELEX for efficient screening of flexible aptamers.

We describe a simple, high-speed, high-throughput aptamer screening for a group of small molecules using graphene oxide (simple Multi-GO-SELEX) without immobilizing targets. The affinities of ten different ssDNA aptamers successfully obtained for three pesticides were in the range of 10-100 nM. Besides a specific aptamer for each target, we found a couple of flexible multi-target aptamers, which can bind with 2 or 3 different molecules. These flexible aptamers developed for binding with a mixture of targets are not only significant for the rapid screening of a group of small molecules but also offer great promise for aptamer-based biosensor applications.

An ultra-sensitive colorimetric detection of tetracyclines using the shortest aptamer with highly enhanced affinity.

A shortened 8-mer ssDNA aptamer was successfully truncated for four different tetracyclines with high affinity. The ultrasensitive colorimetric detection of oxytetracycline using this shortened aptamer was possible, which was about 500-fold enhanced compared to that obtained using the original 76-mer aptamer.

Detection of VR-2332 strain of porcine reproductive and respiratory syndrome virus type II using an aptamer-based sandwich-type assay.

Porcine reproductive and respiratory syndrome virus (PRRSV) causes porcine reproductive and respiratory syndrome disease (PRRS), a disease that has a significant and economic impact on the swine industry. In this study, single-stranded DNA (ssDNA) aptamers with high specificity and affinity against VR-2332 strain of PRRSV type II were successfully obtained. Of 19 candidates, the LB32 aptamer was found to be the most specific and sensitive to VR-2332 strain according to an aptamer-based surface plasmon resonance (SPR) analysis. The detection of VR-2332 of PRRSV type II was successfully accomplished using the enzyme-linked antibody-aptamer sandwich (ELAAS) method. The detection limit of ELAAS was 4.8 × 10(0) TCID(50)/mL that is comparable to some of the previous reports of the PCR-based detection but does not require any complicated equipment or extra costs. Moreover, this ELAAS-based PRRSV detection showed similar sensitivity for both the VR-2332 samples spiked in diluted swine serum and in buffer. Therefore, this VR-2332 strain-specific aptamer and its assay method with high specificity can be used as an alternative method for the fast and precise detection of PRRSV.