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We report herein the design of a strip-based rapid test utilizing bioinspired hybrid nanomaterials for the in situ and at site detection of the drug scopolamine (SCP) using a smartphone for readout, allowing SCP identification in diluted saliva down to 40 nM in less than 15 min. For this purpose, we prepared a nanosensor based on mesoporous silica nanoparticles loaded with a fluorescent reporter (rhodamine B) and functionalized with bethanechol, a potent agonist of recombinant human muscarinic acetylcholine receptor M2 (M2-AChR). M2-AChR interaction with the anchored bethanechol derivative leads to capping of the pores. The sensing mechanism relies on binding of SCP to M2-AChR resulting in pore opening and delivery of the entrapped rhodamine B reporter. Moreover, the material was incorporated into strips for lateral-flow assays coupled to smartphone readout, giving fast response time, good selectivity, and exceptional sensitivity. In an attempt to a mobile analytical test system for law enforcement services, we have also developed a dualplex lateral flow assay for SCP and 3,4-methylenedioxypyrovalerone (MDPV) also known as the so-called “cannibal drug”.
Probe 1, which contains an anilinopyridine chromophore and an azaoxa macrocyclic subunit, presented an absorption band centered at 340 nm in acetonitrile. Addition of Fe(III), Cr(III) and Hg(II) induced the growth of a new absorption band at 430 nm (with color change from colorless to yellow), whereas in the presence of Cu(II), Zn(II) and Pb(II), less marked changes were observed. The color changes observed upon addition of Fe(III), Cr(III) and Hg(II) were ascribed to the formation of 1:1 stoichiometry complexes with probe 1. Coordination of Fe(III), Cr(III) and Hg(II) with the pyridine fragment of 1 induced an enhancement of the charge transfer character accompanied with a marked bathochromic shift that was reflected in a color change from colorless to yellow. The strength of the interaction between probe 1 and Fe(III) cation was modulated upon interaction with anions. Of all the anions tested, only cyanide was able to induce the bleaching of the yellow 1·Fe(III) complex solution. This bleaching was ascribed to
the formation of 1·Fe(III)-CN complex that restored, to some extent, the optical features of the free probe allowing the chromogenic sensing of cyanide. Besides, 1·Fe(III) complex was used to detect
cyanide in acetonitrile-water 90:10 v/v mixtures with good recoveries.
Supramolecular interactions are vital processes in many chemical sensors, biochemical assays, and other analytical detection schemes. On the background of the current, rapidly developing, and constantly changing requirements for (bio)analytical techniques, the classical molecular host is increasingly overburdened to accomplish a specific analytical task with the desired selectivity and sensitivity. Instead, other signaling strategies have to be conceived that overcome the limits in signal output, dynamic range, or compound targeting, which are imminent to various traditional methods. A very promising approach is the combination of concepts of supramolecular chemistry with nanostructured or nanoscopic inorganic materials, that is, the development of hybrid sensor materials. Such hybrids often lead to improved functionality and enhanced performance, and the present chapter discusses the contributory features in relation to the major aspects, which are related to the enhanced coordination by the preorganization of binding sites, signal amplification by the preorganization on surfaces, aggregation‐mediated signaling, surface‐modification‐based signaling, the tuning of selectivity through polarity and size, and gated signaling.
Design strategies for (bio)chemical systems that are inspired by nature's accomplishments in system design and operation on various levels of complexity are increasingly gaining in importance. Within the broad field of biomimetic chemistry, this article highlights various attempts toward improved and sophisticated sensory materials that rely on the combination of supramolecular (bio)chemical recognition principles and nanoscopic solid structures. Examples range from more established concepts such as hybrid sensing ensembles with improved sensitivity and selectivity or for target analytes for which selectivity is hard to achieve by conventional methods, which were often inspired by protein binding pockets or ion channels in membranes, to very recent approaches relying on target-gated amplified signalling with functionalised mesoporous inorganic supports and the integration of native biological sensory species such as transmembrane proteins in spherically supported bilayer membranes. Besides obvious mimicry of recognition-based processes, selected approaches toward chemical transduction junctions utilizing artificially organized synapses, hybrid ensembles for improved antibody generation and uniquely colour changing systems are discussed. All of these strategies open up exciting new prospects for the development of sensing concepts and sensory devices at the interface of nanotechnology, smart materials and supramolecular (bio)chemistry.
This review highlights how the combination of supramolecular principles and nanoscopic solid structures enables the design of new hybrid sensing ensembles with improved sensitivity and/or selectivity and for the targeting of analytes for which selectivity is hard to achieve by conventional methods. Such ideas are bridging the gap between molecules, materials sciences and nanotechnology. Relevant examples will be detailed, taking into account functional aspects such as (1) enhanced coordination of functionalized solids, (2) enhanced signalling through preorganization, (3) signalling by assemblydisassembly of nanoscopic objects, (4) biomimetic probes utilizing discrimination by polarity and size and (5) distinct switching and gating protocols. These strategies are opening new prospects for sensor research and signalling paradigms at the frontier between nanotechnology, smart materials and supramolecular chemistry.