Efficient fluorescence energy transfer system between fluorescein isothiocyanate and CdTe quantum dots for the detection of silver ions

In situ characterization techniques of protein corona around nanomaterials

Nanoparticles (NPs) inevitably interact with proteins upon exposure to biological fluids, leading to the formation of an adsorption layer known as the "protein corona". This corona imparts NPs with a new biological identity, directly influencing their interactions with living systems and dictating their fates in vivo. Thus, gaining a comprehensive understanding of the dynamic interplay between NPs and proteins in biological fluids is crucial for predicting therapeutic effects and advancing the clinical translation of nanomedicines. Numerous methods have been established to decode the protein corona fingerprints. However, these methods primarily rely on prior isolation of NP-protein complex from the surrounding medium by centrifugation, resulting in the loss of outer-layer proteins that directly interact with the biological system and determine the in vivo fate of NPs. We discuss here separation techniques as well as in situ characterization methods tailored for comprehensively unraveling the inherent complexities of NP-protein interactions, highlighting the challenges of in situ protein corona characterization and its significance for nanomedicine development and clinical translation.

The ratiometric fluorescent sensor based on the mixture of CdTe quantum dots and graphene quantum dots for quantitative analysis of silver in drinks

Silver nanoparticles can be used in antibacterial packaging or disinfection. Research has shown that sugary fluid induces the leaching of silver nanoparticles into water, which may be harmful to humans. Single wavelength fluorescence analysis has been used for quantitative analysis of silver nanoparticles but suffers from low specificity and poor anti-interference ability. In this paper, a ratiometric fluorescence sensor system (GCS) was used for the detection of Ag+, which realized both visual detection and quantitative analysis of silver in drinks. The color changes of GCS with different concentrations of Ag+ are distinguishable and easy to analyze. There is also a good linear relationship between the concentrations of Ag+ and varieties of F424 nm/F570 nm, and the lowest detection limit reached 0.2266 nmol/L. This GCS shows good selectivity and recovery and could be used for the detection of Ag+ in drink samples.

A functional cobalt-organic framework constructed by triphenylamine tricarboxylate: Detect nitroaromatics by fluorescence sensing and UV-shielding

Luminescent metal-organic frameworks (LMOF) with ligand-modified are a promising strategy to be applied to fabricate chemical sensors. Herein, a novel Co (II) metal-organic framework (Co-MOF), namely Co [(NTB) bpy] (NTB = 4,4'4″-tricarboxylic acid triphenylamine, bpy = 4,4 '-bipyridyl), was successfully synthesized with excellent water stability and fluorescence properties. Due to the propeller structure of NTB ligands, a special topological structure of Co-MOF was shown: {2⁴.4¹⁶.6⁸}{2}4. It was proved that Co-MOF has great stability by soaking in different solvents for two weeks. Remarkably, the fluorescence quenching experiment verified that Co-MOF has excellent fluorescence sensor performance. Trinitrophenol, 2,4-dinitrophenol, and 2-amino-4-nitrotoluene (10^-5 M) with LOD of 9.00 × 10^-5, 5.40 × 10^-5 and 5.07 × 10^-6 M can be detected via the process of fluorescence enhancement and quenching. Throughout the investigation, the mechanics of fluorescence quenching was performed. Due to the excellent UV absorption capacity of Co-MOF, it was a promising application to combine low-dimensional nanomaterials with sustainable biomass materials. A hybrid films of Co-MOF and cellulose acetate (CA) was generated. The hybrid films had highly transparency in the visible wavelength range and excellent UV-shielding ability owing to the CA/Co-MOF hybrid films enhanced the UV absorption capacity of Co-MOF.

Trace Explosive Detection Based on Photonic Crystal Amplified Fluorescence

With increasing demand for public security and environmental protection, it is highly desirable to develop strategies to identify trace explosives (e. g., 2,4,6-trinitrotoluene (TNT)). Herein, we report novel photonic crystal (PC)-based sensor chips for trace TNT detection by using amplification effect of PCs on fluorescence (FL) signals. The sensor chips are constructed by integrating silica nanoparticles (NPs) modified with (3-aminopropyl)triethoxysilane (APTES) and fluorescein isothiocyanate isomer (FITC) and PC substrates. The amino groups on FITC-APTES-silica NPs can specifically bind with TNT molecules to form Meisenheimer complexes and strongly quench the FL signal of neighboring fluorophores FITC through Förster resonance energy transfer. PCs with matched PBG can amplify the FL signal of FITC-APTES-silica NPs about 24.4-fold and significantly improve sensitivity and resolution of trace TNT detection with the limit of detection of 0.23 nM. The PC-based sensor chips are stable, sensitive, and reliable TNT sensing platforms, showing great potential in homeland safety and environmental protection.

Molecularly imprinted probe based on CdTe QDs and magnetic nanoparticles for selective recognition of malachite green in seawater and its sensing mechanisms

A magnetic molecularly imprinted probe (MMIP@QD) was synthesized by reverse microemulsion method using CdTe QDs, Fe₃O₄, and molecularly imprinted polymer as the fluorophore, magnetic carrier, and recognition sites, respectively. The nanoparticle was characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and vibrating sample magnetometry (VSM). In the optimal experimental condition, fluorescent emission intensity (measured at excitation wavelengths of 350 nm) was quenched linearly with increasing malachite green (MG) concentration from 0.8 to 28.0 μM with LOD of 0.67 μM. Simultaneously, it was observed that the maximum absorption wavelength was blue shifted gradually with the increase of MG concentration. The inner filter effect, static quenching, and band gap transition were interpreted as the mechanisms of fluorescence quenching and wavelength shift. Thermodynamic studies indicated that the quenching reaction proceeded spontaneously. The developed sensor was applied to detect MG in seawater samples. Satisfactory recoveries of MG in spiked seawater ranged from 83.6 to 122.1% with RSD < 1.8%.

Nuclear fast red-based colorimetric sensors for sensitive and selective detection of Ag ions

The reduction of nuclear fast red (NFR) stain by sodium tetrahydroboron was catalyzed in the presence of silver ions (Ag⁺ ). The fluorescence properties of reduced NFR differed from that of NFR. The product showed fluorescence emission at 480 nm with excitation at 369 nm. Furthermore, the fluorescence intensity of the mixture increased strongly in the presence of Ag⁺ and Britton-Robinson buffer at pH 4.78. There was a good linear relationship between increased fluorescence intensity (ΔI) and Ag⁺ concentration in the range 5.0 × 10^-9 to 5.0 × 10^-8  M. The correlation coefficient was 0.998, and the detection limit (3σ/k) was 1.5 × 10^-9  M. The colour of the reaction system changed with variation in Ag⁺ concentration over a wide range. Based on the colour change, a visual semiquantitative detection method for recognition and sensing of Ag⁺ was developed for the range 1.0 × 10^-8  to 5.0 × 10^-4  M, with an indicator that was visible to the naked eye. Therefore, a sensitive, simple method for determination of Ag⁺ was developed. Optimum conditions for Ag⁺ detection, the effect of other ions and the analytical application of Ag⁺ detection of synthesized sample were investigated.

Highly sensitive detection of acid phosphatase by using a graphene quantum dots-based förster resonance energy transfer

A novel and effective fluorescence strategy was developed for sensitive and selective detection of acid phosphatase (ACP). A förster resonance energy transfer (FRET) biosensor was established by attaching nile red (NR) to graphene quantum dots (GQDs) via lecithin/β-Cyclodextrin (lecithin/β-CD) complex as the linker. The introduction of lecithin/β-CD would brought GQDs-NR pair close enough through both electrostatic interaction and hydrophobic interaction, thereby making the FRET occur and thus resulting in the fluorescence quenching of GQDs (donor) and meanwhile the fluorescence enhancement of NR (acceptor). The presence of ACP in the sensing system would catalyze the hydrolysis of lecithin into two parts, resulting in the GQDs-NR pair separation. Meanwhile, considerable fluorescence recovery of GQDs and decreasing of NR was observed due to the inhibition of FRET progress. In this method, the limit of detection (LOD) is 28µUmL^-1 which was considerably low for ACP detection. Using the GQDs-based fluorescence biosensor, we successfully performed in vitro imaging of human prostate cancer cells.

Multifunctional nanoprobe for cancer cell targeting and simultaneous fluorescence/magnetic resonance imaging

Multifunctional nanoprobes with distinctive magnetic and fluorescent properties are highly useful in accurate and early cancer diagnosis. In this study, nanoparticles of Fe3O4 core with fluorescent SiO2 shell (MFS) are synthesized by a facile improved Stöber method. These nanoparticles owning a significant core-shell structure exhibit good dispersion, stable fluorescence, low cytotoxicity and excellent biocompatibility. TLS11a aptamer (Apt1), a specific membrane protein for human liver cancer cells which could be internalized into cells, is conjugated to the MFS nanoparticles through the formation of amide bond working as a target-specific moiety. The attached TLS11a aptamers on nanoparticles are very stable and can't be hydrolyzed by DNA hydrolytic enzyme in vivo. Both fluorescence and magnetic resonance imaging show significant uptake of aptamer conjugated nanoprobe by HepG2 cells compared to 4T1, SGC-7901 and MCF-7 cells. In addition, with the increasing concentration of the nanoprobe, T2-weighted MRI images of the as-treated HepG2 cells are significantly negatively enhanced, indicating that a high magnetic field gradient is generated by MFS-Apt1 which has been specifically captured by HepG2 cells. The relaxivity of nanoprobe is calculated to be 11.5 mg(-1)s(-1). The MR imaging of tumor-bearing nude mouse is also confirmed. The proposed multifunctional nanoprobe with the size of sub-100 nm has the potential to provide real-time imaging in early liver cancer cell diagnosis.

Förster resonance energy transfer properties of a new type of near-infrared excitation PDT photosensitizer: CuInS2/ZnS quantum dots-5-aminolevulinic acid conjugates

Recently, near-infrared (NIR) excitation has been suggested for PDT improvement and therapy of cancer.