Abstract
We present herein the use of nanoporous anodic alumina (NAA) as a suitable support to implement “molecular gates” for sensing applications. In our design, a NAA support is loaded with a fluorescent reporter (rhodamine B) and functionalized with a short single-stranded DNA. Then pores are blocked by the subsequent hybridisation of a specific cocaine aptamer. The response of the gated material was studied in aqueous solution. In a typical experiment, the support was immersed in hybridisation buffer solution in the absence or presence of cocaine. At certain times, the release of rhodamine B from pore voids was measured by fluorescence spectroscopy. The capped NAA support showed poor cargo delivery, but presence of cocaine in the solution selectively induced rhodamine B release. By this simple procedure a limit of detection as low as 5 × 10−7 M was calculated for cocaine. The gated NAA was successfully applied to detect cocaine in saliva samples and the possible re-use of the nanostructures was assessed. Based on these results, we believe that NAA could be a suitable support to prepare optical gated probes with a synergic combination of the favourable features of selected gated sensing systems and NAA.
Highlights
The combination of different inorganic solids with organic compounds has resulted in the preparation of an almost unlimited number of new supports with a wide range of new functionalities
Advantage of nanoporous anodic alumina (NAA) over other systems for cargo release is that their structure is stable and does not degrade or erode in aqueous solutions, which may contribute to the development of robust reproducible devices, most of them for biosensing applications[29,30,31]
The NAA support was obtained according to reported procedures[55]
Summary
Preparation and characterization of the sensing support. The NAA support was obtained according to reported procedures[55]. The FESEM images of the S3 support clearly showed the presence of an organic layer that covered most pores The presence of this organic layer evidenced the suitable consecutive loading, functionalization and capping steps, while the visualisation of the porous framework in certain areas (see the arrow in Fig. 2b) confirmed the preservation of the nanoporous structure in S3. As depicted, the release of rhodamine B from S4 in the absence (Fig. 3, curve c) and presence of cocaine (Fig. 3, curve d) was the same as that obtained for support S3 in the absence of the analyte This result confirmed the requirement of using a specific cocaine-aptamer to cap the NAA support pores to prepare selective probe S3. In another step, the response of S3 to different concentrations of cocaine was studied.
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Published Version
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