Plasmon-enhanced fluorescence for ellagic acid detection based on surface structure of gold nanoparticles.

Ellagic acid (EA), as a natural polyphenolic acid, is considered a naturally occurring inhibitor of carcinogenesis. Herein, we developed a plasmon-enhanced fluorescence (PEF) probe for EA detection based on silica-coated gold nanoparticles (Au NPs). A silica shell was designed to control the distance between silica quantum dots (Si QDs) and Au NPs. The experimental results indicated that an 8.8-fold fluorescence enhancement was obtained compared with the original Si QDs. Three-dimensional finite-difference time-domain (3D-FDTD) simulations further demonstrated that the local electric field enhancement around Au NPs led to the fluorescence enhancement. In addition, the fluorescent sensor was applied for the sensitive detection of EA with a detection limit of 0.14 µM. It can be used to detect EA in pomegranate rind with a recovery rate of 100.26-107.93%. It can also be applied to the analysis of other substances by changing the identification substances. These experimental results indicated that the probe provides a good option for clinical analysis and food safety.

Silica quantum dots; an optical nanosensing approach for trace detection of pesticides in environmental and biological samples.

Both the environment and human health have suffered as a result of excessive and irrational pesticide use. The human body is vulnerable to a wide range of illnesses brought on by prolonged exposure to or intake of food contaminated with pesticide residues, including immunological and hormonal abnormalities and the development of certain tumors. Sensors based on nanoparticles stand out from more conventional spectrophotometry analytical methods due to their low detection limits, high sensitivity, and ease of use; that is why the demand for simple, fast, and less expensive sensing methods increases daily and presents myriad uses. Such demands are fulfilled by employing paper-based analytical devices having intrinsic properties. The presented work reports an on-site, easy-to-handle, and disposable paper-based sensing device for performing fast screening along with readout from a smartphone. The fabricated device utilizes luminescent silica quantum dots, immobilized into a paper cellulose matrix, and the resonance energy transfer phenomenon is employed. The silica quantum dots probes were fabricated from citric acid and, by undergoing physical adsorption, were confined on the nitrocellulose substrate in small wax-traced spots. The silica quantum dots were excited by smartphone ultraviolet LED, acting as an energy source and for capturing the image. The obtained LOD is 0.054 µM, and the coefficient of variation is less than 6.1%, comparable to the result obtained by UV-Visible and fluorometric analysis under similar experimental conditions. In addition, high reproducibility (≥9.8%) and high recovery ≥90% were obtained in spiked blood samples. The fabricated sensor sensitively detected pesticides giving a LOD of 2.5 ppm along with the development of yellow color within a short period of 5 min. The sensor functions well when sophisticated instrumentation is not accessible. The presented work shows the potential of the paper strip for the on-site detection of pesticides in biological and environmental samples.

Sensing and bioimaging of lead ions in intracellular cancer cells and biomedical media using amine-functionalized silicon quantum dots fluorescent probe.

A novel amine-functionalized silica quantum dots (SiQDs) fluorescent nanoprobe was developed for sensing of lead concentration in water, plasma and cell lysate. In addition, the developed probe was utilized for bioimaging of intracellular lead ions in HT 29 cancer cells. The amine-functionalized nanoprobe exhibited fluorescence emission at 445 nm under excitation at 355 nm. Upon addition of lead ions, the fluorescence of SiQDs linearly enhanced from 50 ng/mL to 5 µg/mL and 50 ng/mL to 25 µg/mL for plasma and standard media, respectively. The synthesis and fabrication of this probe are simple and serves high sensitivity with a limit of detection down to around 20 ng/mL. In the presence of various molecular and ion interfering, reliable results are obtained, confirming the specificity of the nanoprobe for lead ion detection. Meanwhile, amine-functionalized SiQD-based nanoprobe exhibits excellent cell membrane-permeability and biocompatibility. Thus, this probe is utilized for lead tracing in HT 29 cancer live cells. Fluorescent microscopy results confirmed the attachment of the produced nanomaterials to the HT 29 cancer cells.

Target-responsive ratiometric fluorescent aptasensor for OTA based on energy transfer between [Ru(bpy)3]2+ and silica quantum dots.

A ratiometric fluorescent aptasensor based on energy transfer between [Ru(bpy)3]2+ and silica quantum dots (silica QDs) for assaying OTA was fabricated. The aptamer for OTA was used as the gate to shield the fluorescent reagent [Ru(bpy)3]2+ into mesoporous silica nanoparticle (MSN). In the presence of OTA, the constrained [Ru(bpy)3]2+ was released from MSN due to a target-induced aptamer conformational change. The released [Ru(bpy)3]2+ adsorbed onto the negatively charged silica QDs through electrostatic interaction. This creates appearance of fluorescence from [Ru(bpy)3]2+ at 625 nm and decrease of the fluorescence from silica QDs at 442 nm owing to the energy transfer. The value of FL625nm/FL442nm was in proportion to the concentration of OTA in the range 0.5~100 ng mL-1 with a LOD of 0.08 ng mL-1. Practical applicability of this method was validated by the determination of OTA in flour samples. Graphical abstract The sensing principle of this sensor.

One-pot ultrafast preparation of silica quantum dots and their utilization for fabrication of luminescent mesoporous silica nanoparticles.

Silica quantum dots (SiQDs) and their luminescent composites have displayed great potential for biomedical applications owing to their chemical inert and low cost. In this work, we report a facile, cost-effective and ultrafast strategy to prepare a stable luminescent SiQDs using N-[3-(trimethoxysilyl)propyl]ethylenediamine (EDAS) and salicylaldehyde as precursors for the first time. These luminescent SiQDs were further utilized for fabrication of luminescent mesoporous silica nanoparticles (MSNs) through direct encapsulation of SiQDs by MSNs. The novel synthetic and modified SiQDs uses commercial raw materials and the entire reaction can be completed within 30 s. The successful preparation of SiQDs and SiQDs@MSNs were characterized by various characterization equipments. The cell viability as well as cell uptake behavior of SiQDs@MSNs were also examined to evaluate their potential for biomedical applications. We demonstrated that these SiQDs@MSNs are low toxicity and of great potential for biological imaging. Based on the above results, we believe that these SiQDs@MSNs should be novel and promising candidates for biomedical applications owing to their intense fluorescence, biocompatibility and high specific surface areas.

Uptake of silica covered Quantum Dots into living cells: Long term vitality and morphology study on hyaluronic acid biomaterials.

Quantum Dots (QDs) are promising very bright and stable fluorescent probes for optical studies in the biological field but water solubility and possible metal bio-contamination need to be addressed. In this work, a simple silica-QD hybrid system is prepared and the uptake in bovine chondrocytes living cells without any functionalization of the external protective silica shield is demonstrated. Moreover, long term treated cells vitality (up to 14days) and the transfer of silica-QDs to the next cell generations are here reported. Confocal fluorescence microscopy was also used to determine the morphology of the so labelled cells and the relative silica-QDs distribution. Finally, we employ silica-QD stained chondrocytes to characterize, as proof of concept, hydrogels obtained from an amphiphilic derivative of hyaluronic acid (HA-EDA-C18) functionalized with different amounts of the RGD peptide.