Fluorescence Of Silicon Quantum Dots Research Articles

Multi-signal aptasensor for thrombin detection based on catalytically active gold nanoparticles and fluorescent silicon quantum dots.

A multi-signal aptasensor for thrombin determination isproposed based on catalytically active gold nanoparticles (AuNPs) and fluorescent silicon quantum dots (SiQDs). Yellow 4-Nitrophenol (4-NP) could be converted to colorless 4-Aminophenol (4-AP) by catalytically active aptamer-modified AuNPs (S1-AuNPs). The SiQDs emitted strong blue fluorescence at 455nm at the excitation wavelength of 367nm. When thrombin was absent, S1-AuNPs could catalytically reduce yellow 4-NP to colorless 4-AP. When thrombin was added, the aptamer could be transformed into a G-quadruplex structure, which masked the surface-active catalytic sites of AuNPs and restrained the reduction of 4-NP. Thus, the fluorescence of SiQDs was greatly quenched by 4-NP through the inner filter effect (IFE), and the solution color remained yellow. As the concentration of thrombin increased, the catalytic activity of S1-AuNPs decreased. The concentration of 4-NP that was converted to 4-AP declined and the unconverted 4-NP increased. In this process, the absorption peak of 4-NP at 400nm increased while the fluorescence emission of SiQDs at 455nm decreased. The linear ranges of the fluorometric and colorimetric aptasensor were 0.5-30nM and 0.3-30nM, respectively. The limits of detection (LOD) for the two modes were 0.15nM and 0.13nM. Furthermore, a portable sensing platform was constructed by combining the smartphone-based device with the software ImageJ for the determination of thrombin. With the advantages of cost-effectiveness, simplicity of operation and broad applicability, this aptasensor provided a new perspective for on-site determinationof thrombin in the clinical field.

A Ratiometric Fluorescent Sensor Based on Silicon Quantum Dots and Silver Nanoclusters for Beef Freshness Monitoring

A ratiometric fluorescent sensor with hydrogen sulfide (H2S) and methanthiol (CH3SH) sensitivity was developed to real-time monitor beef freshness. A silicon quantum dots (SiQD) and silver nanoclusters (AgNC) complex, namely SiQD-AgNC, was used as the dual emission fluorescence materials. Due to the fluorescence resonance energy transfer (FRET) effect between SiQD and AgNC, when the fluorescence of AgNC (610 nm) was quenched by H2S or CH3SH, the fluorescence of SiQD (468 nm) recovered, resulting in an increase of the fluorescent intensity ratio (I468/I610). I468/I610 showed a linear relationship with the H2S concentration within the concentration range of 1.125-17 μM, with a limit of detection (LOD) value of 53.6 nM. Meanwhile, I468/I610 presented two linear relationships with the CH3SH concentration within the concentration range of 1.125-17 μM and 23.375-38.25 μM, respectively, with a LOD value of 56.5 nM. The SiQD-AgNC complex was coated on a polyvinylidene fluoride (PVDF) film to form a portable SiQD-AgNC/PVDF film sensor. This film showed purplish red-to-cyan color changes in response to H2S and CH3SH, with LOD values of 224 nM and 233 nM to H2S and CH3SH, respectively. When the film was used to monitor beef freshness at 4 °C, its fluorescent color gradually changed from purplish red to cyan. Hence, this study presented a new ratiometric fluorescent sensor for intelligent food packaging.

CoOOH nanosheets ensure ratiometric fluorescence assay of acetylcholinesterase

Cobalt oxyhydroxide nanosheets (CoOOH) with peroxidase-like activity provide a promising probe for acetylcholinesterase (AChE) sensing through a ratiometric fluorescence strategy. Fluorescence of silicon quantum dots (SiQDs) at 457 nm was quenched by CoOOH on account of inner-filter effect (IFE). Meanwhile, the nonfluorescent o-phenylenediamine (OPD) was catalytically oxidized to 2,3-diaminophenazine (oxOPD) by CoOOH nanosheets with emission at 572 nm. The acetylcholine (ATCh) was catalytically hydrolyzed by AChE to enzymatic thiocholine (TCh), which decomposed CoOOH to Co2+, recovered the fluorescence of SiQDs and reduced the emission of oxOPD. Fluorescence ratio at F457/F572 serves as signal output for AChE detection within 5 × 10−5–0.05 and 0.05–10 U mL−1, with a limit of detection (LOD) of 3.2 × 10−5 U mL−1. The sensing strategy was applied for AChE assay in human blood and erythrocyte.

Fluorescence determination of lactate dehydrogenase activity based on silicon quantum dots

Silicon quantum dots (SiQDs) synthesized based on 3-aminopropyltrimethoxysilane (ATPMS) as silicon source were used to detect the activity of lactate dehydrogenase (LDH) through changes of fluorescence intensity of SiQDs. In this system, the fluorescence of SiQDs was first quenched by nicotinamide adenine dinucleotide (NADH), and then recovered with the addition of LDH, as NADH was consumed by catalytic reaction of LDH. A linear calibration chart of LDH is obtained in the range of 0.77–385 U/mL. The assay displays high selectivity towards LDH detection, and was successfully applied to the analysis of LDH in human serum samples. This assay has great prospects for the diagnosis and prognosis of various diseases, especially melanoma.

A “switch-on” fluorescence assay based on silicon quantum dots for determination of ascorbic acid

Water dispersible silicon quantum dots (SiQDs) showing blue fluorescence were synthesized with 3-aminopropyltriethoxysilane (APTES) as silicon source. Based on the synthesized SiQDs as the photoluminescence unit, MnO2 nanosheets (NS) as the quencher, a “switch-on” fluorescence assay for the determination of ascorbic acid (AA) was designed. The fluorescence of SiQDs can be effectively quenched by MnO2 NS because of the internal filtration effect. In the presence of AA, MnO2 is reduced to Mn2+, so that the fluorescence of SiQDs is partially recovered. The recovered fluorescence intensity was related to the concentration of AA. Under the optimal experimental conditions, the linear response range of the assay to AA is 1–80 µM, and the detection limit is 0.48 µM. The method for the determination of AA has the advantages of simple, low cost, good selectivity and sensitivity. The assay has been successfully applied to the quantification of AA in beverage (mizone) samples, which proves the practicability of the assay.

Promoted off-on recognition of H2O2 based on the fluorescence of silicon quantum dots assembled two-dimensional PEG-MnO2 nanosheets hybrid nanoprobe.

An "off-on" assay system for H2O2 determination was developed based on assembling ultra-bright fluorescent silicon quantum dots (SiQDs) and PEG-MnO2 nanosheets. Among them, SiQDs acted as fluorometric reporter, which can effectively eliminate the interference of plant pigments under excitation of 365nm. PEG-MnO2 nanosheets played dual function of nanoquencher and H2O2 recognizer. Unlike previous reports, the quenching mechanism of SiQDs by PEG-MnO2 nanosheets is attributed to both the associative effect of inner filter effect and the static quenching effect. Thus, the fluorescence intensity of SiQDs at 445nm decreased with increasing concentration of PEG-MnO2 nanosheets. After addition of H2O2, PEG-MnO2 nanosheets were reduced to Mn2+, consequently resulting in the recovery of the SiQDs fluorescence. Combined with these properties, an off-on fluorescent method was built for determination of H2O2 in plant leaves with high sensitivity and selectivity. The present method has two linear ranges: from 0.05 to 1μM with a detection limit of 0.09μM and from 1 to 80μM with a detection limit of 4.04μM. Graphical abstract Schematic representation of the mechanism of SiQD/PEG-MnO2 nanoprobe for determination of H2O2.

Highly sensitive and selective "off-on" fluorescent sensing platform for ClO- in water based on silicon quantum dots coupled with nanosilver.

We present a new "off-on" fluorescence probe for detecting hypochlorite (ClO-) based on silicon quantum dots coupled with silver nanoparticles (SiQDs/AgNPs) as nanocomplexes. Via introducing N-[3-(trimethoxysilyl)propyl]ethylenediamine and catechol as initial reactants, silicon quantum dots (SiQDs) with excellent properties were synthesized through a simple hydrothermal method. Transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of quantum dots. The fluorescence of SiQDs could be quenched by the silver nanoparticles (AgNPs) by surface plasmon-enhanced energy transfer (SPEET) from SiQDs (donor) to AgNPs (acceptor). The AgNPs could be etched by adding ClO-, thus freeing the SiQDs from the AgNP surfaces and restoring the SiQDs' fluorescence. The sensing system exhibits many advantages, such as wide linear response range, high sensitivity, and excellent selectivity. Under optimized conditions, wide linear ranges (from 0.1 to 100.0μM) and low detection limits (0.08μM) were obtained for ClO-. Graphical Abstract.

Silicon quantum dot-coated onto gold nanoparticles as an optical probe for colorimetric and fluorometric determination of cysteine.

Silicon quantum dots (SiQDs) were synthesized from N-[3-(trimethoxysilyl)propyl]-ethylenediamine and catechol by a hydrothermal method. Transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of quantum dots. The SiQDs were then placed on gold nanoparticles (AuNPs). When Cys is added to this solution, Cys will penetrate the SiQDs "shell" of the SiQDs/AuNP composite. This is due to the interaction and conformational differences of Cys and other substance with AuNPs and leads to the dispersion of the aggregated SiQD/AuNPs. A color change from purple to red can be visually observed, and the (green) fluorescence of SiQDs (with excitation/emission peaks at 430/520nm) is restored. This dual-readout nanoprobe was successfully applied to the selective and sensitive detection of cysteine (Cys) in (spiked) serum and urine samples. The detection limit is 3.5nmol·L-1 (at an S/N ratio of 3), and the method works on the 0.01 to 2μM Cys concentration range. Graphical abstract Schematic illustration of a method forsynthesizing silicon quantum dots (SiQDs) and coating them on gold nanoparticles (AuNPs) as an optical probe for colorimetric and fluorometric determination of cysteine.

“Turn on-off” fluorescent sensor for protamine and heparin based on label-free silicon quantum dots coupled with gold nanoparticles

An ultrasensitive “turn on-off” fluorescent sensor was presented for determination of protamine and heparin based on the high quenching ability of gold nanoparticles (AuNPs) to the fluorescence of silicon quantum dots (SiQDs) as well as high binding affinity of protamine with heparin. The fluorescence of SiQDs was quenched significantly by adding AuNPs into SiQDs solution. Upon addition of protamine, the AuNPs aggregated and the fluorescence of SiQDs was recovered due to the competitive adsorption of protamine and SiQDs on AuNPs. Addition of heparin disturbed the interaction between protamine and AuNPs due to its strong affinity to protamine, resulting in an adsorption of SiQDs on the surface of AuNPs. Thus the fluorescence of SiQDs was quenched. The strategy was simply achieved by measuring the changes in the fluorescence of SiQDs. The research results suggested that the developed method has several advantages such as label-free, high sensitivity, low cost, ease of operation. The linear response range was obtained over the range 0–1.2μg/mL and 0.002–1.4μg/mL with the low detection limit of 6.7ng/mL and 0.67ng/mL for protamine and heparin, respectively. The sensing platform was successfully applied to determination of heparin and protamine in serum samples.

Label-free silicon quantum dots as fluorescent probe for selective and sensitive detection of copper ions

In this work, label-free silicon quantum dots (SiQDs) were used as a novel fluorescence probe for the sensitive and selective detection of Cu2+. The fluorescence of the SiQDs was effectively quenched by H2O2 from the reaction of ascorbic acid with O2, and hydroxyl radicals from Fenton reaction between H2O2 and Cu+. The fluorescence intensity of SiQDs was quenched about 25% in 15min after the addition of H2O2 (1mM). While the SiQDs was incubated with AA (1mM) and Cu2+ (1µM) under the same conditions, the fluorescence intensity of SiQDs decreased about 55%. Obviously, the recycling of Cu2+ in the test system may lead to a dramatical decrease in the fluorescence of SiQDs. Under the optimized experimental conditions, the rate of fluorescence quenching of SiQDs was linearly dependent on the Cu2+ concentration ranging from 25 to 600nM with the limit of detection as low as 8nM, which was much lower than that of existing methods. Moreover, the probe was successfully applied to the determination of Cu2+ in different environmental water samples and human hair.