Abstract
In the present study, invertase-mediated nanogold clusters were synthesized on onion membranes, and their application for sucrose biosensor fabrication was investigated. Transmission electron microscopy revealed free nanoparticles of various sizes (diameter ~5 to 50 nm) along with clusters of nanogold (~95 to 200 nm) on the surface of inner epidermal membranes of onions (Allium cepa L.). Most of the polydispersed nanoparticles were spherical, although some were square shaped, triangular, hexagonal or rod-shaped. Ultraviolet–visible spectrophotometric observations showed the characteristic peak for nanoparticles decorated invertase-onion membrane at approximately 301 nm. When excited at 320 nm in the presence of sucrose, the membranes exhibited a photoemission peak at 348 nm. The fluorescence lifetime of this nanogold modified onion membrane was 6.20 ns, compared to 2.47 ns for invertase-onion membrane without nanogold. Therefore, a sucrose detection scheme comprised of an invertase/nanogold decorated onion membrane was successfully developed. This fluorescent nanogold-embedded onion membrane drop-test sensor exhibited wide acidic to neutral working pH range (4.0-7.0) with a response time 30 seconds (<1 min). The fabricated quenching-based probe had a low detection limit (2x10−9 M) with a linear dynamic range of 2.25x10−9 to 4.25x10−8 M for sensing sucrose. A microplate designed with an enzyme-nanomaterial-based sensor platform exhibited a high compliance, with acceptable percentage error for the detection of sucrose in green tea samples in comparison to a traditional method. With some further, modifications, this fabricated enzyme-nanogold onion membrane sensor probe could be used to estimate glucose concentrations for a variety of analytical samples.Graphical abstractSynthesis and characterization of invertase assisted nanogold clusters on onion membranes and their application for fluorescence-based sucrose sensor.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-015-0089-1) contains supplementary material, which is available to authorized users.
Highlights
Metal nanoparticles are outstanding building blocks for fabrication of biosensors, due to their surface plasmon resonance shifts in response to a biorecognition event
After incubating the onion membrane with invertase and gold chloride solution for 96 h, the absorption peak shifted from 275 to 301 nm, which indicated that there was a direct reaction among gold chloride, invertase and onion membrane to form nanogold clusters (NAuCs)
The sensor was based on formation of invertase-induced nanogold clusters and particles within the membrane
Summary
Metal nanoparticles are outstanding building blocks for fabrication of biosensors, due to their surface plasmon resonance shifts in response to a biorecognition event. Properties of nanoparticles vary in accordance with their size and composition, which facilitates diverse applications in various areas including catalysis, sensors and medicine. Production of nanoparticles can be achieved through chemical, physical or biological methods. There has been considerable attention focused on biological methods for synthesis of metallic nanoparticles, as there is a vast array of biological. Enzyme-guided nanoparticles have been used for fabrication of biosensors that can detect prostate-specific antigen (a biomarker of prostate cancer), with outstanding sensitivity. The development of optical sensors using enzyme-stimulated synthesis of metallic nanoparticles has been reported by Willner et al [4]. In the presence of bovine serum albumin, bacterial protease
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