Fluorescent aptasensor for highly sensitive detection of Staphylococcus aureus based on dual-amplification strategy by integrating DNA walking and hybridization chain reaction.

Food-borne diseases caused by bacteria threaten human health. Herein, we presented a new fluorescent aptasensor by coupling DNA walking and hybridization chain reaction (HCR) for convenient and sensitive quantification of bacteria. Staphylococcus aureus (S. aureus) was selected as target. When there was target in the system, the binding of S. aureus with its aptamer caused the disintegration of aptamer/DNA walker on the surface of AuNPs and released DNA walker. With the help of Nt.BsmAI, DNA walker moved along the surface of AuNPs and trigger probe was detached from AuNPs. The trigger probe could initiate hybridization chain reaction (HCR) and opened the stems of H1@AuNPs probe and H2@AuNPs probe. After the addition of nicking endonuclease, the adjacent upconversion nanoparticles (UCNPs, NaYF4:Yb3+, Er3+) were further away from the quenchers (AuNPs) of H1 and H2. Therefore, the fluorescence intensity of UCNPs could be restored via fluorescence resonance energy transfer (FRET). Bacteria were thus detected by recording the fluorescence intensity of UCNPs. This method is simple, rapid and sensitive. It can directly detect bacteria in a low background signal. The limit of detection (LOD) was 10 CFU/mL, detection time was less than 3 h. Recovery rates in simulated milk, honey and human serum samples ranged from 93.6 % to 105.8 %. The strategy opens up new paths for early diagnosis of diseases and food monitoring.

Combat biofilm by bacteriostatic aptamer-functionalized graphene oxide.

Biofilms are the main reason for a large number deaths and high health costs. Their better protection compared to planktonic form against conventional antibiotics leads to poor treatment efficiency. Nanoagent-targeted delivery is a promising avenue for disease therapeutic, but its application targeting biofilms has not been reported currently. The roles, if any, of aptamers acting as delivery carrier and targeting factor, the graphene oxide (GO), and GO modified with aptamers against biofilms were then systematically evaluated. Here, we successfully developed an aptamer-targeted GO strategy against biofilms. We investigated the efficacy of aptamer-GO conjugates by UV spectrophotometer, inverted microscopy, and atomic force microscopy; 93.5 ± 3.4% Salmonella typhimurium biofilms were inhibited and 84.6 ± 5.1% of biofilms were dispersed by a ST-3-GO conjugate. More importantly, this conjugate represented distinctively toxicity to S. typhimurium. Thus, this strategy significantly displays excellent antibiofilm properties and may serve as a long-term solution for biofilm control.

Influence of aptamer-targeted antibiofilm agents for treatment of Pseudomonas aeruginosa biofilms.

Biofilms are bacterial communities consisting of numerous extracellular polymeric substances. Infections caused by biofilm-forming bacteria are considered to be a major threat to health security and so novel approaches to control biofilm are of importance. Aptamers are single-strand nucleic acid molecules that have high selectivity to their targets. Single-walled carbon nanotubes (SWNTs) are common nanomaterials and have been shown to be toxic to bacterial biofilms. The aim of this study was to test whether an aptamer could play a role as targeting agents to enhance the efficiency of anti-biofilm agents. Hence, two complexes (aptamer-SWNTs and aptamer-ciprofloxacin-SWNTs) based on an aptamer which targets Pseudomonas aeruginosa and SWNTs were constructed. Both complexes were assessed against P. aeruginosa biofilms. In vitro tests demonstrated that the aptamer-SWNTs could inhibit ~36% more biofilm formation than SWNTs alone. Similarly, the aptamer-ciprofloxacin-SWNTs had a higher anti-biofilm efficiency than either component or simple mixtures of two components. Our study underscores the potential of aptamers as targeting agents for anti-biofilm compounds, as well as providing a new strategy to control biofilms.