Highly sensitive chemosensor for detection of methamphetamine by the combination of AIE luminogen and cucurbit[7]uril

Highlights

• Obtained a new functional self-assembly product CB[7]⊃TPPE.

• The CB[7]⊃TPPE could highly selective and sensitive detection of methamphetamine in methanol with broad concentration.

• The obtained test strips can quickly detect methamphetamine by the naked eye.

Abstract

Methamphetamine (METH) abuse has become a global problem, and new strategies for rapid and sensitive detection of METH are in urgent need. Herein, a novel technique is developed for highly sensitive detection of METH in solution with a broad concentration range by the assembly of AIE luminogen of tetrakis(4-(pyridin-4-yl)phenyl)ethene (TPPE) and cucurbit[7]uril (CB[7]). The ¹H NMR and isothermal titration calorimetry (ITC) characterizations confirm that TPPE and CB[7] are self-assembled in a ratio of 1:4. While, the interaction of CB[7] with METH exhibits a binding ratio of 1:1 and stronger binding ability than with TPPE. Based on the competitive binding affinity, CB[7]⊃TPPE could be used as a chemosensor to detect METH in solution, which exhibits remarkable advantages such as rapid response, high sensitivity and low limit of detection (LOD). When the concentration of METH solution is larger than 40 μM, the enhancement of fluorescence intensity and change of fluorescent colour could be directly observed upon UV irradiation. When the METH solution concentration is higher than 10 μM, we can use our fabricated test strips to rapidly and visibly detect. If above detections do not work, we can measure the photoluminescence (PL) spectra of the sensing system, which shows a LOD as low as 0.43 μM. This unique CB[7]⊃TPPE based chemosensor is potentially applicable in real-time and visual detection of METH in solution and provides a powerful platform for preventing chemical solvent transport.

Introduction

It is well known that frequent and long-term drugs abuse will cause drug addiction and other serious diseases such as mental illness, insomnia, depression and violent tendencies [[1], [2], [3]]. Over the years, the kinds, amounts, and compositions of illegal drugs have varied with suppliers, finances, and consumers’ choice [4]. New psychoactive substances (NPSs), as the most common drugs in young people, are becoming difficult to be detected, analysed, and controlled [[5], [6], [7]]. As a group of NPSs, methamphetamine (METH) is now being abused more seriously than ever [8]. According to the reports, seizures of METH doubled in the five years prior to 2017 [9]. Among them, the diversification of METH transport methods has become the culprit of its flooding. At present, common transport methods include human drug trafficking, animal drug trafficking, chemical solvent drug trafficking, etc. Compared with biological transport, using methanol and alcohol solutions as drug trafficking has become the main mode of transport method due to its simple operation, security and difficult detection [10]. To prevent this mode of transport spreading and METH abuse, detection techniques including gas chromatography/mass spectrometry (GC/MS) [11], liquid chromatography/mass spectrometry (LC/MS) [12], capillary electrophoresis [13], immunoassays [14], molecularly imprinted polymer solid-phase extraction [15], etc. have been developed. However, these analytic methods are relatively expensive, time consuming, and require well-trained workers. Therefore, development of a new strategy to rapidly and sensitively detect METH especially its solutions becomes more and more urgent in this field.

Compared with the conventional methods, fluorescent technique has been proven to be a promising alternative for detection of METH and related NPSs drugs due to the advantages of simple design, easy operation, high sensitivity and so on [[16], [17], [18]]. However, conventional fluorophores, such as fluorescein and rhodamine [19,20], are highly emissive in solution but their fluorescence is usually quenched upon enhancement of concentration or aggregation. In other words, they suffer from the aggregation-caused quenching (ACQ) effect [21,22], which has greatly limited their applications as probes. Exactly opposite to the ACQ fluorophores, luminogenic materials with aggregation-induced emission (AIE) [[23], [24], [25], [26]] features show intense emission in both aggregate and solid states although they are weakly or non-emissive in their solutions, making the design of robust and portable fluorescent probes for METH detection much convenient. Tetraphenylethene (TPE) and its derivatives, as the classical AIE luminogens (AIEgens), have been widely used for the construction of powerful AIE probes due to its distinct advantages, such as high efficiency of solid-state emission, simple synthetic procedures, and easy functionalization [[27], [28], [29]]. However, the use of AIEgens together with host molecules, such as cucurbit[n]urils (CB[n]) via supramolecular interactions as fluorescent probes is rarely reported [30].

As a supramolecular host, CB[n] are made up dimethyl bridged glycoluril, and contain a hydrophobic cavity and ionic-dipole [31]. The hydrogen bonding interaction between the carbonyl and guest molecules in CB[n] make them prefer to associate with neutral molecules or charged guest molecules [[32], [33], [34], [35], [36]]. Due to their excellent trapping properties, CB[n] have been widely used in host-guest chemistry [[37], [38], [39], [40]], molecular self-assembly [[41], [42], [43], [44]], etc. In particular, cucurbit[7]uril (CB[7]) not only exhibits good binding ability but also has excellent water solubility, which enables it to be applicable in aqueous system [[45], [46], [47]]. Nonetheless, to the best of our knowledge, the guest-host complexes of AIEgens and CB[n] have not been used as probes for illegal drugs detection.

Herein, we developed a new type of probe by integrating AIEgen of tetrakis(4-(pyridin-4-yl)phenyl) ethylene (TPPE) and CB[7] (CB[7]⊃TPPE) for METH detection in its solution state with high sensitivity and selectivity. The results indicate that CB[7]⊃TPPE exhibits a rapid and selective response toward METH in solution with broad concentration range, and the limit of detection can reach as low as 0.43 μM. This work thus provides a convenient sensing technique for METH in its solution with high sensitivity, which is potentially useful for practical application.