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Pathogenic bacteria cause serious harm to human health, which calls for the development of advanced detection methods. Herein, we developed a novel detection platform based on fluorescence resonance energy transfer (FRET) for rapid, ultrasensitive and specific bacteria detection, where gold nanoparticles (AuNPs, acceptor) were conjugated with aptamers while upconversion nanoparticles (UCNPs, donor) were functionalized with corresponding complementary DNA (cDNA). The spectral overlap between UCNPs fluorescence emission and AuNPs absorption enables the occurrence of FRET when hybridizing the targeted aptamer and cDNA, causing upconversion fluorescence quenching. In the presence of target bacteria, the aptamers preferentially bind to bacteria forming a three-dimensional structure and thereby dissociate UCNPs-cDNA from AuNPs-aptamers, resulting in the recovery of upconversion fluorescence. Using the UCNPs based FRET aptasensor, we successfully detected Escherichia coli ATCC 8739 (as a model analyte) with a detection range of 5–10 6 cfu/mL and detection limit of 3 cfu/mL. The aptasensor was further used to detect E. coli in real food and water samples (e.g., tap/pond water, milk) within 20 min. The novel UCNPs based FRET aptasensor could be used to detect a broad range of targets from whole cells to metal ions by using different aptamer sequences, holding great potential in environmental monitoring, medical diagnostics and food safety analysis. [ABSTRACT FROM AUTHOR]

Abstract: Aptamers, single-stranded nucleic acids, provide a unique opportunity as amplifiable molecules using polymerase chain reaction (PCR) as well as recognition molecules like antibodies. We report a highly sensitive detection of Escherichia coli by taking advantage of the aptamer amplification as well as the specific binding of aptamers onto E. coli. This unique approach consists of three steps. First, the target E. coli was captured by antibody-conjugated magnetic beads. Second, the RNA aptamers were bound onto the surface of captured E. coli in a sandwich way. Finally, the heat-released aptamers were amplified by using real-time reverse-transcriptase-PCR (RT-PCR). The aptamer amplification in this approach has enabled a sensitive detection of microorganisms, such as the detection of 10 E. coli in 1ml sample. When compared to the amplification of nucleic acids extracted from the target microorganisms, this approach can not only prevent the loss of target nucleic acids during the sample preparation by obviating the necessity of cell lysis, but also provide an additional mechanism of signal amplification due to the binding of many aptamers to the surface of each E. coli. Detection of E. coli in this approach showed a wide dynamic range from 101 to 107 E. coli per ml, which can be explained by the exponential amplification of aptamers. This report has demonstrated, for the first time, the effective use of aptamer amplification in the development of sensitive microorganism detection. It is anticipated that the present approach will be easily expanded and employed in various types of microorganism detection. [Copyright &y& Elsevier]