Quenched or alive quantum dots: The leading roles of ligand adsorption and photoinduced protonation

All-quantum dot based Förster resonant energy transfer: key parameters for high-efficiency biosensing

While colloidal quantum dots (QDs) are commonly used as fluorescent donors within biosensors based on Förster resonant energy transfer (FRET), they are hesitantly employed as acceptors. On the sole basis of Förster theory and the well-known behaviour of organic dyes, it is often argued that the QD absorption band over the UV-visible range is too wide. Discarding these preconceptions inherited from classical fluorophores, we experimentally examine the FRET process occurring between donor and acceptor CdTe QDs and provide a mathematical description of it. We evidence that the specific features of QDs unexpectedly lead to the enhancement of acceptors' emission (up to +400%), and are thus suitable for the design of highly efficient all-QD based FRET sensors. Our model enables us to identify the critical parameters maximizing the contrast between positive and negative biosensing readouts: the concentrations of donors and acceptors, their spectral overlap, the densities of their excitonic states, their dissipative coupling with the medium and the statistics of QD-QD chemical pairing emerge as subtle and determinant parameters. We relate them quantitatively to the measured QD-QD FRET efficiency and discuss how they must be optimized for biosensing applications.

Microfluidic fluorescent platform for rapid and visual detection of veterinary drugs

The overuse of veterinary drugs and veterinary drug residues is increasingly becoming an obstacle to sustainable development worldwide. It is therefore imperative to establish a quantitative, sensitive and efficient method for the detection of veterinary drugs. Herein, we developed a visual microfluidic detection platform for rapid and sensitive detection of veterinary drugs using CdTe quantum dots (QDs) with three different ligands as the sensing units. Green-emissive 3-mercaptopropionic acid (MPA)-CdTe QDs, yellow-emissive thioglycolic acid (TGA)-CdTe QDs and orange-emissive N-acetyl-l-cysteine (NAC)-CdTe QDs were synthesized by a sulfhydryl aqueous phase method. These CdTe QDs show selective rapid fluorescence response to pefloxacin (PEF), malachite green (MG), and 1-aminohydantoin hydrochloride (AHD). With the concentration of veterinary drugs increasing, the CdTe QDs reveals a fluorescence color variation from bright to dark until quenched and the response degree of CdTe QDs with different ligands to veterinary drugs is different. Specifically, the limits of detection (LODs) of MPA-CdTe, TGA-CdTe and NAC-CdTe QDs probes for PEF were 7.57 μM, 1.75 μM and 2.90 μM, respectively, and the response was complete in a few seconds, realizing the sensitive and rapid detection of PEF. The three kinds of CdTe QDs could also be used in the detection of other veterinary drugs such as MG and AHD. Finally, a microfluidic detection platform was constructed for visual sensing and rapid detection towards veterinary drugs. The sensor platform holds the advantages of simple operation, low cost, rapid sensing and good sensitivity, and is potentially useful for visual quantitative detection of veterinary drug residues in aquatic products and the environment.