Self-aggregated nanoparticles of cholesterol-modified glycol chitosan conjugate: Preparation, characterization, and preliminary assessment as a new drug delivery carrier

Cholesterol-modified glycol chitosan (CHGC) conjugate was synthesized and characterized by FTIR and ¹H NMR. The degree of substitution (DS) was 6.7 cholesterol groups per 100 sugar residues of glycol chitosan. CHGC formed self-aggregated nanoparticles with a roughly spherical shape and a mean diameter of 228 nm by probe sonication in aqueous medium. The physicochemical properties of the self-aggregated nanoparticles were studied using dynamic light scattering (DLS), transmission electron microscopy (TEM) and fluorescence spectroscopy. The critical aggregation concentration (CAC) of self-aggregated nanoparticles in aqueous solution was 0.1223 mg/mL. Indomethacin (IND), as a model drug, was physically entrapped into the CHGC nanoparticles by dialysis method. The characteristics of IND-loaded CHGC (IND-CHGC) nanoparticles was analyzed using DLS, TEM and high performance liquid chromatography (HPLC). The IND-CHGC nanoparticles were almost spherical in shape and their size increased from 275 to 384 nm with the IND-loading content increasing from 7.14% to 16.2%. The in vitro release behavior of IND from CHGC nanoparticles was studied by a dialysis method in phosphate buffered saline (PBS, pH 7.4). IND was released in a biphasic way. The initial rapid release in 2 h and slower release for up to 12 h were observed. The results indicated that CHGC nanoparticles had a potential as a drug delivery carrier.     

Development of functionalized terbium fluorescent nanoparticles for antibody labeling and time-resolved fluoroimmunoassay application

Silica-based functionalized terbium fluorescent nanoparticles were prepared, characterized and developed as a fluorescence probe for antibody labeling and time-resolved fluoroimmunoassay. The nanoparticles were prepared in a water-in-oil (W/O) microemulsion containing a strongly fluorescent Tb³⁺ chelate, N,N,N¹,N¹-[2,6-bis(3′-aminomethyl-1′-pyrazolyl)phenylpyridine] tetrakis(acetate)-Tb³⁺ (BPTA-Tb³⁺), Triton X-100, octanol, and cyclohexane by controlling copolymerization of tetraethyl orthosilicate (TEOS) and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEPS) with ammonia water. The characterizations by transmission electron microscopy and fluorometric methods show that the nanoparticles are spherical and uniform in size, 45 ± 3 nm in diameter, strongly fluorescent with fluorescence quantum yield of 10% and a long fluorescence lifetime of 2.0 ms. The amino groups directly introduced to the nanoparticle’s surface by using AEPS in the preparation made the surface modification and bioconjugation of the nanoparticles easier. The nanoparticle-labeled anti-human α-fetoprotein antibody was prepared and used for time-resolved fluoroimmunoassay of α-fetoprotein (AFP) in human serum samples. The assay response is linear from 0.10 ng ml⁻¹ to about 100 ng ml⁻¹ with the detection limit of 0.10 ng ml⁻¹. The coefficient variations (CVs) of the method are less than 9.0%, and the recoveries are in the range of 84-98% for human serum sample measurements.     

Ultrasensitive determination of silver ion based on synchronous fluorescence spectroscopy with nanoparticles

Based on the characteristics of synchronous fluorescence spectroscopy (SFS), a new method with high sensitivity and selectivity was developed for rapid determination of silver ion with functional cadmium sulphide (CdS) nanoparticles as a fluorescence probe. When Δλ (λ_em − λ_ex) = 215 nm, maximum synchronous fluorescence is produced at 304 nm. Under optimal conditions, functional cadmium sulphide displayed a calibration response for silver ion over a wide concentration range from 0.8 × 10⁻¹⁰ to 1.5 × 10⁻⁸ mol L⁻¹. The limit of detection was 0.4 × 10⁻¹⁰ mol L⁻¹ and the relative standard deviation of seven replicate measurements for the lowest concentration (0.8 × 10⁻¹⁰ mol L⁻¹) was 2.8%. Compared with several fluorescence methods, the proposed method had a wider linear range and improved the sensitivity. Furthermore, the concentration dependence of the synchronous fluorescence intensity is effectively described by a Langmuir-type binding isotherm.     

Preparation, characterization and evaluation of water-soluble l-cysteine-capped-CdS nanoparticles as fluorescence probe for detection of Hg(II) in aqueous solution

Water-soluble l-cysteine-capped-CdS nanoparticles were prepared in aqueous solution at room temperature through a straightforward one-pot process by using safe and low-cost inorganic salts as precursors, and characterized by transmission electron microscopy, X-ray diffraction spectrometry, Fourier transform infrared spectrometry, spectrofluorometry and ultraviolet-visible spectrometry. The prepared l-cysteine-capped-CdS nanoparticles were evaluated as fluorescence probe for Hg(II) detection. The fluorescence quenching of the l-cysteine-capped-CdS nanoparticles depended on the concentration and pH of Hg(II) solution. Maximum fluorescence quenching was observed at pH 7.4 with the excitation and emission wavelengths of 360 nm and 495 nm, respectively. Quenching of its fluorescence due to Hg(II) at the 20 nmol l⁻¹level was unaffected by the presence of 5 × 10⁶-fold excesses of Na(I) and K(I), 5 × 10⁵-fold excesses of Mg(II), 5 × 10⁴-fold excesses of Ca(II), 500-fold excesses of Al(III), 91-fold excesses of Mn(II), 23.5-fold excesses of Pb(II), 25-fold excesses of Fe(III), 25-fold excesses of Ag(I), 8.5-fold excesses of Ni(II) and 5-fold excesses of Cu(II). Under optimal conditions, the quenched fluorescence intensity increased linearly with the concentration of Hg(II) ranging from 16 nmol l⁻¹ to 112 nmol l⁻¹. The limit of detection for Hg(II) was 2.4 nmol l⁻¹. The developed method was applied to the detection of trace Hg(II) in aqueous solutions.     

Preparation and application of functionalized nanoparticles of CdSe capped with 11-mercaptoundecanoic acid as a fluorescence probe

A new fluorescence probe, CdSe nanocrystal has been prepared and modified with 11-mercaptoundecanoic acid [HS-(CH₂)₁₀-COOH]. The functionalized nanoparticles were characterized using transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy. The results demonstrate that CdSe is dispersed homogeneously in aqueous solution and well protected from the environmental oxygen. They can be used as a new fluorescence probe for lysozyme, which was simple, rapid and specific. Under the optimum condition, the response is linearly proportional to the amount of lysozyme from 0.20 to 26.0 μg ml⁻¹, and the limit of detection is 0.115 μg ml⁻¹. The proposed method has been applied to the determination of lysozyme in egg white, with the recovery of 96-105%.     

Enoxacin-Tb complex as an environmentally friendly fluorescence probe for DNA and its application

The fluorescence intensity of the enoxacin (ENX)-Tb³⁺ complex enhanced by DNA was studied. On the basis of this study, an environmentally friendly fluorescence probe of enoxacin-Tb³⁺ for the determination of single-stranded and double-stranded DNA was developed. Under the optimal conditions, the enhanced fluorescence intensity was in proportion to the concentration of DNA in the range of 2.0 × 10⁻⁸ to 2.0 × 10⁻⁶ g mL⁻¹ for hsDNA, 1.0 × 10⁻⁸ to 1.0 × 10⁻⁶ g mL⁻¹ for ctDNA and 5.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g mL⁻¹ for thermally denatured ctDNA. The detection limits (S/N = 3) were 5.0, 9.0 and 3.0 ng mL⁻¹, respectively. The interaction modes between ENX-Tb³⁺ and DNA and the mechanism of the fluorescence enhancement were also discussed in details. The experimental results from UV absorption spectra, fluorescence spectra and the competing combination tests between the ENX-Tb³⁺ complex and EB probe indicated that the possible interaction modes between enoxacin-Tb³⁺ complex and DNA had at least two different binding modes: the electrostatic binding and the intercalation binding. Additionally, this fluorescence probe was used to study the interaction between heavy metals and DNA.     

Self-aggregated nanoparticles from methoxy poly(ethylene glycol)-modified chitosan: synthesis; characterization; aggregation and methotrexate release in vitro

Methoxy poly(ethylene glycol)-grafted-chitosan (mPEG-g-CS) conjugates were synthesized by formaldehyde linking method and characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (¹H-NMR). The degree of substitution (DS) of methoxy poly (ethylene glycol) (mPEG) in the mPEG-g-CS molecules determined by ¹H-NMR ranged from 19% to 42%. The critical aggregation concentration (CAC) was determined by fluorescence spectroscopy using pyrene as fluorescence probe and its value was 0.07 mg/mL in water. mPEG-g-CS formed monodisperse self-aggregated nanoparticles with a roughly spherical shape and a mean diameter of 261.9 nm were prepared by the dialysis method. mPEG-g-CS self-aggregated nanoparticles were used as carriers of poorly water-soluble anticancer drug methotrexate (MTX). MTX was physically entrapped inside mPEG-g-CS self-aggregated nanoparticles by dialysis method and the characteristics of MTX-loaded mPEG-g-CS self-aggregated nanoparticles were analyzed using dynamic laser light scattering (DLLS), transmission electron microscopy (TEM). Moreover, in vitro release behavior of MTX was also investigated and the results showed that MTX was continuously released more than 50% in 48 h.     

Highly sensitive and selective detection of biothiols using graphene oxide-based “molecular beacon”-like fluorescent probe

A fluorometric method for quantity analysis of biothiols was developed using a graphene oxide (GO)-based “molecular beacon”-like probe, which consisted of FITC labeled thymine (T)-rich single-stranded DNA (ssDNA), GO and Hg²⁺ ions. The labeled ssDNA containing T–T mismatches would self-hybridize to duplex in the presence of Hg²⁺, which can avoid its adsorption on GO and the fluorescence of this GO-based probe was recovered. The fluorescence of the probe quenched after the addition of biothiols such as glutathione (GSH) and cysteine (Cys) owing to thiol groups can selectively competitive ligation of Hg²⁺ ions with T–T mismatches. In the present work, the GO-based probe was used for the determination of GSH and Cys. Under the optimal conditions, a linear correlation was established between fluorescence intensity ratio I₀/I and the concentration of GSH in the range of 2.0 × 10⁻⁹–5.0 × 10⁻⁷ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁹ mol L⁻¹. The linear range for Cys is from 5.0 × 10⁻⁹ to 4.5 × 10⁻⁷ mol L⁻¹ with a detection limit of 2.0 × 10⁻⁹ mol L⁻¹. The proposed method was applied to the determination of GSH in human serum and cell extract samples with satisfactory results.     

Preparation and application of functionalized nanoparticles of CdS as a fluorescence probe

CdS nanoparticles have been prepared and modified with mercaptoacetic acid. The functionalized nanoparticles are water-soluble and biocompatible. They could be used as a fluorescence probe in the determination of bovine serum albumin (BSA), which was proved to be a simple, rapid and specific method. In comparison with single organic fluorophores, these nanoparticle probes are brighter, more stable against photobleaching, and do not suffer from blinking. Under the optimum conditions, the response is linearly proportional to the concentration of BSA between 0.1 and 3.2 μg ml⁻¹, and the limit of detection is 0.08 μg ml⁻¹.     

Photoinduced interactions between colloidal TiO2 nanoparticles and calf thymus-DNA

The interaction of colloidal TiO₂ nanoparticles with calf thymus-DNA was studied by using absorption, FT-IR, steady state and time resolved fluorescence spectroscopic techniques. The apparent association constant has been deduced (K_app = 2.85 × 10³ M⁻¹) from the absorption spectral changes of the DNA-colloidal TiO₂ nanoparticles using the Benesi–Hildebrand equation. Addition of colloidal TiO₂ nanoparticles quenched the fluorescence of EtBr–DNA. The number of binding sites (n = 0.97) and the apparent binding constant (K = 6.68 × 10³ M⁻¹) were calculated from relevant fluorescence quenching data. The quenching, through a static mechanism, was confirmed by time resolved fluorescence spectroscopy.     

A novel fluorescence probe for cilnidipine assay

A general route for preparation of dye-encapsulated polymer particles via an emulsion polymerization process has been described. 1-Naphthaleneboronic acid (NBA) was encapsulated, the resultant particles were used as a fluorescence probe for cilnidipine assay based on fluorescence quenching. The sensitivity of NBA-encapsulated probe to cilnidipine was largely improved in comparison with that of free NBA. The probe showed a linear response toward cilnidipine over the concentration range of 2.0 × 10⁻⁷ to 1.1 × 10⁻⁵ mol l⁻¹, with high sensitivity, fast response time, and good selectivity.     

Fluorescence enhancement of CdTe/CdS quantum dots by coupling of glyphosate and its application for sensitive detection of copper ion

A novel fluorescent probe for Cu²⁺ determination based on the fluorescence quenching of glyphosate (Glyp)-functionalized quantum dots (QDs) was firstly reported. Glyp had been used to modify the surface of QDs to form Glyp-functionalized QDs following the capping of thioglycolic acid on the core–shell CdTe/CdS QDs. Under the optimal conditions, the response was linearly proportional to the concentration of Cu²⁺ between 2.4 × 10⁻² μg mL⁻¹ and 28 μg mL⁻¹, with a detection limit of 1.3 × 10⁻³ μg mL⁻¹ (3δ). The Glyp-functionalized QDs fluorescent probe offers good sensitivity and selectivity for detecting Cu²⁺. The fluorescent probe was successfully used for the determination of Cu²⁺ in environmental samples. The mechanism of reaction was also discussed.     

A novel fluorescence sensor based on covalent immobilization of 3-amino-9-ethylcarbazole by using silver nanoparticles as bridges and carriers

A novel technique of covalent immobilization of indicator dyes in the preparation of fluorescence sensors is developed. Silver nanoparticles are used as bridges and carriers for anchoring indicator dyes. 3-amino-9-ethylcarbazole (AEC) was employed as an example of indicator dyes with terminal amino groups and covalently immobilized onto the outmost surface of a quartz glass slide. First, the glass slide was functionalized by (3-mercaptopropyl) trimethoxysilane (MPS) to form a thiol-terminated self-assembled monolayer, where silver nanoparticles were strongly bound to the surface through covalent bonding. Then, 16-mercaptohexadecanoic acid (MHDA) was self-assembled to bring carboxylic groups onto the surface of silver nanoparticles. A further activation by using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) converted the carboxylic groups into succinimide esters. Finally, the active succinimide esters on the surface of silver nanoparticles were reacted with AEC. Thus, AEC was covalently bound to the glass slide and an AEC-immobilized sensor was obtained. The sensor exhibited very satisfactory reproducibility and reversibility, rapid response and no dye-leaching. Rutin can quench the fluorescence intensity of the sensor and be measured by using the sensor. The linear response of the sensor to rutin covers the range from 2.0 × 10⁻⁶ to 1.5 × 10⁻⁴ mol L⁻¹ with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹. The proposed technique may be feasible to the covalent immobilization of other dyes with primary amino groups.     

Dendrimer-rhodium nanoparticle modified glassy carbon electrode for amperometric detection of hydrogen peroxide

Metallic nanoparticles of rhodium were prepared by using the newly synthesized N,N-bis-succinamide-based dendrimer as stabilizers. The Rh nanoparticles were spherical shaped with a particle size of ∼2 nm. The dendrimer Rh-encapsulated nanoparticles (Rh-DENs) were immobilized on glassy carbon electrode (GCE) and their electrocatalytic activity towards hydrogen peroxide reduction was investigated using cyclic voltammetry and chronoamperometry. The Rh-DENs modified GCE showed excellent electrocatalytic activity for hydrogen peroxide reduction reactions. The steady-state cathodic current response of the modified electrode at −0.3 V (vs SCE) in phosphate buffer (pH 7.0) showed a linear response to hydrogen peroxide concentration ranging from 8 to 30 μM with a detection limit and sensitivity of 5 μM and 0.03103 × 10⁻⁶ A μM⁻¹, respectively.     

Interaction of colloidal AgTiO2 nanoparticles with bovine serum albumin

The interaction between colloidal AgTiO₂ nanoparticles and bovine serum albumin (BSA) was studied by using absorption, steady state, time resolved and synchronous fluorescence spectroscopy measurements. Absorption spectroscopy proved the formation of a ground state BSA?AgTiO₂ complex. Upon excitation of BSA, colloidal AgTiO₂ nanoparticles effectively quenched the intrinsic fluorescence of BSA. The number of binding sites (n = 1.06) and apparent binding constant (K = 3.71 × 10⁵ M⁻¹) were calculated by the fluorescence quenching method. A static mechanism and conformational changes of BSA were observed.     

A novel nonenzymatic fluorescent sensor for glucose based on silica nanoparticles doped with europium coordination compound

Amino-functionalized luminescent silica nanoparticles (LSNPs) doped with the europium(III) mixed complex, Eu(TTA)₃phen with 2-thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline(phen) were synthesized successfully using an revised Stöber method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR), and fluorescence spectroscopy were performed for characterizing the synthesized nanoparticles. In the presence of glucose, the fluorescence intensity of the amino-functionalized LSNPs was enhanced due to the enhanced fluorescence resonance energy transfer. Based on fluorescence-enhancing effect, a simple and sensitive method for the determination of glucose was proposed. Under the optimized experimental conditions, the enhanced fluorescence intensity ratio (ΔF/F₀) was linear with the concentration of glucose (c) in the range of 0.0-180 μg ml⁻¹ with a detection limit of 0.8 μg ml⁻¹ (S/N = 3). The R.S.D. values were 0.33% and 0.37% at the levels of 22.5 and 100 μg ml⁻¹, respectively. The proposed method was applied to the determination of glucose in synthetic samples with satisfactory results. The proposed method was also performed to the analysis of blood glucose in human serum samples and the results were in good agreement with clinical data provided by the hospital, which indicates that the method presented here is not only simple, sensitive, but also reliable and suitable for practical applications.     

Aptamer-functionalized silver nanoparticles for scanometric detection of platelet-derived growth factor-BB

In this work, we reported a scanometric assay system based on the aptamer-functionalized silver nanoparticles (apt-AgNPs) for detection of platelet-derived growth factor-BB (PDGF-BB) protein. The aptamer and ssDNA were bound with silver nanoparticles by self-assembly of sulfhydryl group at 5′ end to form the apt-AgNPs probe. The apt-AgNPs probe can catalyze the reduction of metallic ions in color agent to generate metal deposition that can be captured both by human eyes and a flatbed scanner. Two different color agents, silver enhancer solution and color agent 1 (10 mM HAuCl₄ + 2 mM hydroquinone) were used to develop silver and gold shell on the surface of AgNPs separately. The results demonstrated that the formation of Ag core–Au shell structure had some advantages especially in the low concentrations. The apt-AgNPs probe coupled with color agent 1 showed remarkable superiority in both sensitivity and detection limit compared to the apt-AuNPs system. The apt-AgNPs system also produced a wider linear range from 1.56 ng mL⁻¹ to 100 ng mL⁻¹ for PDGF-BB with the detection limit lower than 1.56 ng mL⁻¹. The present strategy was applied to the determination of PDGF-BB in 10% serum, and the results showed that it had good specificity in complex biological media.     

An rhodamine-based fluorescence probe for iron(III) ion determination in aqueous solution

An “off-on” rhodamine-based fluorescence probe for the selective signaling of Fe(III) has been designed exploiting the guest-induced structure transform mechanism. This system shows a sharp Fe(III)-selective fluorescence enhancement response in 100% aqueous system under physiological pH value and possesses high selectivity against the background of environmentally and biologically relevant metal ions including Al(III), Cd(II), Fe(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I). Under optimum conditions, the fluorescence intensity enhancement of this system is linearly proportional to Fe(III) concentration from 6.0 × 10⁻⁸ to 7.2 × 10⁻⁶ mol L⁻¹ with a detection limit of 1.4 × 10⁻⁸ mol L⁻¹.     

A functionalized gold nanoparticles and Rhodamine 6G based fluorescent sensor for high sensitive and selective detection of mercury(II) in environmental water samples

A gold-nanoparticles (Au NPs)-Rhodamine 6G (Rh6G) based fluorescent sensor for detecting Hg (II) in aqueous solution has been developed. Water-soluble and monodisperse gold nanoparticles (Au NPs) has been prepared facilely and further modified with thioglycolic acid (TGA). Free Rh6G dye was strongly fluorescent in bulk solution. The sensor system composing of Rh6G and Au NPs fluoresce weakly as result of fluorescence resonance energy transfer (FRET) and collision. The fluorescence of Rh6G and Au NPs based sensor was gradually recovered due to Rh6G units departed from the surface of functionalized Au NPs in the presence of Hg(II). Based on the modulation of fluorescence quenching efficiency of Rh6G-Au NPs by Hg(II) at pH 9.0 of teraborate buffer solution, a simple, rapid, reliable and specific turn-on fluorescent assay for Hg(II) was proposed. Under the optimum conditions, the fluorescence intensity of sensor is proportional to the concentration of Hg(II). The calibration graphs are linear over the range of 5.0 × 10⁻¹⁰ to 3.55 × 10⁻⁸ mol L⁻¹, and the corresponding limit of detection (LOD) is low as 6.0 × 10⁻¹¹ mol L⁻¹. The relative standard deviation of 10 replicate measurements is 1.5% for 2.0 × 10⁻⁹ mol L⁻¹ Hg(II). In comparison with conventional fluorimetric methods for detection of mercury ion, the present nanosensor endowed with higher sensitivity and selectivity for Hg(II) in aqueous solution. Mercury(II) of real environmental water samples was determined by our proposed method with satisfactory results that were obtained by atomic absorption spectroscopy (AAS).     

Derivatized silver nanoparticles as sensor for ultra-trace nitrate determination based on light scattering phenomenon

New silver nanoparticles coated with EDTA (EDTA-AgNPs) have been synthesized by citrate reduction method and characterized by UV-vis spectroscopy, molecular fluorescence and scanning electron microscopy (SEM). The derivatized nanoparticles show fluorescent emission and second order scattering (SOS) signals which in presence of nitrate are both attenuated. The SOS decreasing is greater than its fluorescent quenching; considering this fact, a new ultra sensitive methodology using the derivatized silver nanoparticles as sensor for nitrate determination has been developed. Under optimal established conditions, a linear response has been obtained within the range of 6.4 × 10⁻⁴ to 3.0 μg mL⁻¹ nitrate concentrations, with a detection limit of 1.8 × 10⁻⁴ μg mL⁻¹. This novel technique provides a sensitive and selective methodology for nitrate determination and has been satisfactorily applied to its quantification in parenteral solutions.