Wenqi Yang (a), Yuanzheng Cai (a), Hongmei Cai (b), Chenwei Gu (a), Wanzhen Xu (a)(d), Weihong Huang (a)(d), Wenming Yang (c)(d)
(a) School of Emergency Management, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang 212013, China
(b) Taizhou Customs Comprehensive Technical Service Center, Taizhou 225316, China
(c) School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China
(d) Changzhou Engineering and Technology Institute of Jiangsu University, Changzhou 213164, China
## Abstract
Growing concerns about antibiotic residues in food and environmental samples demand the development of highly sensitive and portable detection platforms. Herein, a fluorescent turn-off–on aptasensor was constructed using mercaptopropionic acid (MPA)-capped CdZnTe quantum dots (QDs) and MoS2 nanosheets for ultrasensitive sulfadiazine (SDZ) detection via Förster resonance energy transfer (FRET). The aptamer-conjugated CdZnTe QDs (QDs-apt) served as energy donors, while MoS2 nanosheets acted as quenchers. Upon specific recognition of SDZ, the formation of the aptamer-target complex inhibited the proximity between the QDs-apt and MoS2 nanosheets, inducing dissociation of QDs-apt from the nanosheets surface. This process restored the fluorescence, and the fluorescence intensity was proportional to the concentration of SDZ. The sensor exhibited a wide linear range (0–1000 μM), a low detection limit (3.03 nM), and high specificity against structural analogs. Further integration with a three-dimensional paper-based microfluidic chip enabled smartphone-assisted visual quantification, achieving an on-site detection limit of 56.57 μM. Practical applicability was validated through recovery tests in honey (99–114 %) and river water (98–102.75 %). This work synergistically combined the exceptional fluorescent properties of alloyed QDs, the efficient quenching ability of MoS2, and the portability of paper-based analytics, offering a robust platform for rapid antibiotic monitoring in resource-limited settings.
Graphical abstract
## Introduction
The extensive use of antibiotics in agriculture and animal husbandry has raised concerns about food safety and environmental sustainability. Antibiotics are widely used in livestock to prevent disease and promote growth. However, misuse or overuse often leads to antibiotic residues in animal-derived food products, including meat, dairy, and honey [1], [2]. Long-term exposure to these residues through food consumption can contribute to the emergence of antibiotic resistance in humans, which compromises the efficacy of antibiotic therapies and poses a significant global health challenge [2], [3], [4]. Furthermore, the transmission of antibiotic resistance between humans and animals exacerbates this problem, creating a severe public health threat. In addition to health concerns, antibiotic residues also disrupt aquatic ecosystems by endangering aquatic species, thereby further affecting environmental balance [5]. These complex risks underscore the urgent need for sensitive, efficient, and reliable detection methods to monitor antibiotic residues in food and environmental samples.
Traditional detection techniques, including high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC–MS), are widely regarded as gold standards for antibiotic residue analysis due to their high accuracy and sensitivity [6], [7], [8], [9], [10], [11]. However, these methods face several practical limitations. These methods require expensive and sophisticated instrumentation, skilled operators, and lengthy detection procedures, making them unsuitable for rapid, on-site applications. Moreover, the complex sample preparation steps, including extraction and purification, increase both the time and cost of analysis [12]. Such limitations render these methods more suitable for laboratory-based analysis rather than field-based or real-time monitoring across the food supply chain, where rapid intervention is essential [13], [14]. Moreover, the extensive use of organic solvents and consumables in these techniques poses environmental challenges, further emphasizing the need for more sustainable alternatives.
To address these limitations, innovative detection technologies have emerged as potential solutions, with nanomaterial-enhanced biosensors receiving particular attention [15]. Biosensors utilize biological recognition elements, such as aptamers and antibodies, in combination with physical or chemical transducers to enable rapid, on-site detection of target analytes with minimal instrumentation [16], [17], [18], [19]. Compared to conventional methods, biosensors offer significant advantages, including near-real-time signal transduction (often < 30 min), portability, and field-deployable operation, making them indispensable for high-throughput monitoring of food safety and environmental pollutants [20], [21], [22], [23].
Biosensors are broadly classified into three categories: optical, electrochemical, and physical biosensors [24]. Optical biosensors, the most prevalent type, employ principles such as fluorescence, chemiluminescence, or surface plasmon resonance (SPR) to transduce biomolecular interactions into measurable optical signals, offering high sensitivity, selectivity, and rapid response. For example, a fluorescence biosensor utilizing graphene oxide/gold nanoparticles (GO/AuNPs) achieved a low detection limit of 0.1 pg/mL for aflatoxin B1 (AFB1) [25]. Unlike electrochemical or physical biosensors, optical biosensors require minimal sample pretreatment and enable direct, real-time detection without complex instrumentation. A smartphone-based method integrating UV illumination and RGB analysis demonstrated portable AFB1 detection, validated in real-sample applications [26]. Optical biosensors not only outperform traditional methods in detection efficiency, but also show greater potential and flexibility in applications. Mehdi’s team reviewed the application of a variety of optical sensors based on DNA nanostructures in the detection of food contaminants [27]. Therefore, optical biosensors have made remarkable progress in the fields of food safety detection, environmental monitoring and disease diagnosis, and have broad prospects for development.
Among optical biosensor technologies, quantum dots (QDs) with semiconductor nanocrystals with size-tunable fluorescence, have emerged as highly promising tools for enhancing biosensor performance [28]. QDs are characterized by their unique optoelectronic and fluorescent properties, including high brightness, narrow emission spectra and excellent photostability, outperforming conventional organic fluorophores in sensitivity and signal stability [29], [30], [31], [32]. Notably, alloyed CdZnTe QDs have garnered significant attention due to their superior photostability and biocompatibility compared to binary analogs (e.g., CdTe, CdSe), positioning them as ideal probes for food and environmental analysis [33], [34], [35], [36]. Studies by Liang et al. have demonstrated that CdZnTe QDs exhibit exceptional sensitivity in detecting low concentrations of target molecules [37], [38]. Additionally, Yang et al. have shown that surface functionalization via ligand engineering can further amplify QD sensitivity and selectivity, expanding their utility in complex matrices [39]. A groundbreaking advancement lies in the integration of QDs with Förster resonance energy transfer (FRET) systems. In such system, CdZnTe QDs act as energy donors, paired with MoS2 nanosheets as quenchers, to achieve ratiometric detection. In the absence of the target, the fluorescence of QDs is suppressed by energy transferring to MoS2 nanosheets due to their close proximity. When the target binds, the aptamer changes its structure, causing the QDs to detach from the nanosheet surface. This restores fluorescence, with its intensity directly reflecting the target concentration [40].
In addition to biosensors, paper-based microfluidic chips have emerged as a versatile platform for low-cost, portable, and rapid detection. These chips utilize porous fibrous materials to autonomously transport and separate liquids via capillary action, eliminating the need for external pumps or complex instrumentation [41], [42]. Their simple design and manufacturing processes, often involving screen printing or inkjet printing, make them ideal for large-scale production at low cost, especially in resource-limited settings. Moreover, their integration with portable devices, such as smartphones, enables real-time visualization and interpretation of results, offering significant advantages for on-site applications [43]. Cao et al. demonstrated that by coupling QDs fluorescence signals with smartphone cameras, paper-based microfluidic chips allow for rapid, user-friendly detection with minimal technical requirements, making them highly suitable for monitoring food safety and environmental contamination [44].
In this work, we developed an innovative fluorescent aptasensor that combines alloyed CdZnTe QDs, MoS2 nanosheets that mediated FRET quenching, and a paper-based microfluidic platform to address the critical need for rapid, on-site detection of SDZ residues. By leveraging the enhanced fluorescent properties of Zn-doped CdTe QDs and the high quenching efficiency of MoS2 nanosheets, the developed sensor achieves ultrasensitive SDZ detection via FRET mechanism. Furthermore, to bridge the gap between laboratory analysis and field applicability, a 3D paper-based microfluidic chip was designed for smartphone-assisted visual quantification, eliminating reliance on complex instrumentation. This dual-mode strategy not only overcame the limitations of conventional chromatographic methods but also established a scalable platform for monitoring antibiotic residues in food and environmental samples.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/fluorescent-turn-off-on-aptasensors-with-cdznte-quantum-dots-and-mos2-nanosheets-for-highly-sensitive-detection-of-sulfadiazine-residues.html