LED-compatible fluorosensor for measurement of near-neutral pH values

We report on an optical sensor material suitable for fluorimetric measurement of pH in the 6–9 range using a new, fully LED-compatible fluorescent dye. Its base form has a strong absorption between 580 and 630 nm that matches the emission band of conventional yellow or orange light-emitting diodes. Two kinds of dye immobilization are reported. The first is based on covalent binding to a cellulosic matrix and the resulting material is intended for use in sensing membranes. The second involves physical entrapment of the dye in a sol-gel matrix which can be used for optical fiber tip coating as well as in evanescent wave type sensors. Both kinds of sensor materials are studied with respect to dynamic pH ranges, response times, sensitivity toward ion strength, and stability.Dedicated to Professor G. Werner, Leipzig, on the occasion of his 60th birthday.     

A new water-soluble near-neutral ratiometric fluorescent pH indicator

Donor-pi-acceptor fluorene derivative 1c is a near-neutral pH indicator whose pKa of approximately 7.0 was determined by both absorption and fluorescence methods. 1c satisfies important criteria for a sensitive ratiomeric fluorescent pH indicator with a distinctive isoemissive point, good dispersion in cell cytosol, and low cytotoxicity. Furthermore, its 2PA cross section of 100 GM in its neutral form suggests its potential in two-photon fluorescence imaging applications.     

Fluorescence optical sensors for continuous determination of near-neutral pH values

The preparation and performance of two types of optical sensors for continous measurement of near-neutral pH values are described. the sensors are based on glass-immobilized fluorescent pH indicators and allow the determination of pHs in the range 6.4 to 7.7 with a precision of ±0.01 units. Response times are of the order of 1 min for 99% of the total signal change. Adverse effects of ionic strength are almost completely eliminated by appropriate treatment of the glass surface, thereby creating a well-defined and highly charged environment for the indicator. When the sensing layers are attached to the end of a bifurcated fibre optical light guide, a device for remotely sensing pH values is obtained.     

Conjugated polyelectrolyte amplified fluorescent assays with probe functionalized silica nanoparticles for chemical and biological sensing

Low-cost sensors with high sensitivity and selectivity for chemical and biological detection are of high scientific and economic importance. Silica nanoparticles (NPs) have shown vast promise in sensor applications by virtue of their controllable surface modification, good chemical stability, and biocompatibility. This mini-review summarizes our recent development of silica NP-based assays for chemical and biological detection, where silica NPs serve as the substrate for probe immobilization, target recognition, and separation. The assay performance is further improved through the introduction of conjugated polyelectrolyte to amplify the detection signal. The assays have been demonstrated to be successful for the detection of DNA, small molecules, and proteins. They could be generalized for other targets based on specific interactions, such as DNA hybridization, antibody-antigen recognition, and target-aptamer binding.     

Dual colored mesoporous silica nanoparticles with pH activable rhodamine-lactam for ratiometric sensing of lysosomal acidity

Alteration of lysosome acidity has been implicated in many biological events ranging from apoptosis to cancer metastasis, etc. Mesoporous silica nanoparticles doped with acid activable rhodamine-lactam and fluorescein isothiocyanate (FITC) were developed for ratiometric sensing of lysosomal pH changes in live cells with flow cytometry.     

Ultrasensitive non-enzymatic glucose sensing at near-neutral pH values via anodic stripping voltammetry using a glassy carbon electrode modified with Pt3Pd nanoparticles and reduced graphene oxide

We describe an anodic stripping voltammetric (ASV) method for glucose sensing that widely expands the typical amperometric i-t response of glucose sensors. The electrode is based on a working electrode consisting of a glassy carbon electrode modified with Pt-Pd nanoparticles (NPs; in an atomic ratio of 3:1) on a reduced graphene oxide (rGO) support. The material was prepared via the spontaneous redox reaction between rGO, PdCl₄ ²⁻ and PtCl₄ ²⁻ without any additional reductant or surfactant. Unlike known Pt-based sensors, the use of Pt₃Pd NPs results in an ultrasensitive ASV approach for sensing glucose even at near-neutral pH values. If operated at a working voltage as low as 0.06 V (vs. SCE), the modified electrode can detect glucose in the 2 nM to 300 μM concentration range. The lowest detectable concentration is 2 nM which is much lower than the LODs obtained with other amperometric i-t type sensing approaches, most of which have LODs at a μM level. The sensor is not interfered by the presence of 0.1 M of NaCl.

We describe an anodic stripping voltammetric method for glucose sensing that widely expands the typical amperometric i-t response of glucose sensors (2 nM to 300 μM). The electrode is based on a glassy carbon electrode modified with Pt-Pd nanoparticles on a reduced graphene oxide (rGO) support.

     

Synthesis of ratiometric fluorescent nanoparticles for sensing oxygen

A facile reprecipitation-encapsulation method is used for the preparation of ratiometric fluorescent nanoparticles (NPs) for sensing intracellular oxygen. The surface of the NPs is modified in-situ with poly-L-lysine, which renders good biocompatibility and enables easy internalization into living cells. The sensor NPs contain a red fluorescent probe whose fluorescence is sensitive to oxygen with a quenching response of 77 % on going from nitrogen saturation to oxygen saturation, and a reference dye giving a green signal that acts as an oxygen-independent reference. The ratio of the two emissions serves as the analytical information and is sensitive to dissolved oxygen in the 0–43?ppm concentration range. When incorporated into cells, the ratio of the signals increases by 400?% on going from oxygen-saturated to oxygen-free environment.

Surface-functionalized fluorescent silica nanoparticles for the detection of ATP

The design of two-dyed fluorescent silica nanoparticles for ATP detection is presented. The indicator dye possesses a dipicolyl-amine (DPA) unit complexed with Zn(II) as a receptor function for ATP while a rhodamine derivative is used as the reference dye. The nanoparticles were fully characterized regarding analytical performance, morphology and cytocompatibility.     

Dual fluorescent labelling of cellulose nanocrystals for pH sensing

Cellulose nanocrystals were converted into ratiometric pH-sensing nanoparticles by dual fluorescent labelling employing a facile one-pot procedure. A simple and versatile three-step procedure was also demonstrated extending the number of fluorophores available for grafting. In this method an amine group was introduced via esterification followed by a thiol-ene click reaction.     

Core-shell silica nanoparticles synthesized for quantitative study of DNA cleavage by laser-induced fluorescence microscopy

Dye-doped silica nanoparticles (C dots) were synthesized in reverse microemulsions and used to quantitatively examine DNA cleavage in the presence of transition metal ions. The cores were synthesized as fluorescein isothiocyanate (FITC)-doped silica nanoparticles and the shells' surfaces were modified with single-stranded DNA oligomers tagged with Cy5 fluorophores. DNA cleavage induced by heavy metal ions was estimated by comparing the fluorescence of Cy5 before and after reaction with metal ions. For this, a lab-built laser-induced fluorescence microscope equipped with a charge coupled device (CCD) camera, for imaging, and photomultiplier tube, for photon counting, was used. FITC fluorescence from the core was measured as an internal standard to compensate for possible loss of the beads during the treatment. The cleavage of DNA in air in the presence of Pb(2+), Cd(2+), and Hg(2+) at 1 ng/mL was found to be 14%, 6%, and 20%, respectively, and was significantly reduced to below 9% under N(2) gas, indicating that the main cleavage source was oxygen in air. The most significant DNA cleavage was observed with the addition of hydrogen peroxide. This analytical method using dye-doped C dots provided convenient handling and quantification of the estimation of metal-DNA interaction with a detection limit of 34.9 pmol/mL.     

Hollow mesoporous silica nanoparticles for intracellular delivery of fluorescent dye

In this study, hollow mesoporous silica nanoparticles (HMSNs) were synthesized using the sol-gel/emulsion approach and its potential application in drug delivery was assessed. The HMSNs were characterized, by transmission electron microscopy (TEM), Scanning Electron Microscopy (SEM), nitrogen adsorption/desorption and Brunauer-Emmett-Teller (BET), to have a mesoporous layer on its surface, with an average pore diameter of about 2 nm and a surface area of 880 m²/g. Fluorescein isothiocyanate (FITC) loaded into these HMSNs was used as a model platform to assess its efficacy as a drug delivery tool. Its release kinetic study revealed a sequential release of FITC from the HMSNs for over a period of one week when soaked in inorganic solution, while a burst release kinetic of the dye was observed just within a few hours of soaking in organic solution. These FITC-loaded HMSNs was also found capable to be internalized by live human cervical cancer cells (HeLa), wherein it was quickly released into the cytoplasm within a short period of time after intracellular uptake. We envision that these HMSNs, with large pores and high efficacy to adsorb chemicals such as the fluorescent dye FITC, could serve as a delivery vehicle for controlled release of chemicals administered into live cells, opening potential to a diverse range of applications including drug storage and release as well as metabolic manipulation of cells.     

Stabilising fluorescent silica nanoparticles against dissolution effects for biological studies

Here we show that commonly employed St?ber type fluorescently labelled silica nanoprobes degrade by hydrolytic dissolution, accelerated under biological media conditions as compared to water alone. We have thus developed a method to greatly improve their stability under such conditions.     

Dye-concentrated organically modified silica nanoparticles as a ratiometric fluorescent pH probe by one- and two-photon excitation

Basic dye-concentrated nanoparticles (approximately 33 nm in diameter) show fluorescence-based ratiometric pH response, by one- and two-photon excitations, with improved proton sensing ability (pKa approximately 6.4) through nanoscopic intraparticle energy transfer.     

Core-shell effects of functionalized oxide nanoparticles inside long-range meso-ordered spray-dried silica spheres

Core-shell and homogeneous distributions of functionalized cerium oxide nanoparticles within spray-dried mesostructured silica spheres are achieved by modification of synthesis parameters such as the templating agent and nanoparticle capping functions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Uniform silica nanoparticles encapsulating two-photon absorbing fluorescent dye

We have prepared uniform silica nanoparticles (NPs) doped with a two-photon absorbing zwitterionic hemicyanine dye by reverse microemulsion method. Obvious solvatochromism on the absorption spectra of dye-doped NPs indicates that solvents can partly penetrate into the silica matrix and then affect the ground and excited state of dye molecules. For dye-doped NP suspensions, both one-photon and two-photon excited fluorescence are much stronger and recorded at shorter wavelength compared to those of free dye solutions with comparative overall dye concentration. This behavior is possibly attributed to the restricted twisted intramolecular charge transfer (TICT), which reduces fluorescence quenching when dye molecules are trapped in the silica matrix. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells with low cytotoxicity.     

Naphthalimide-rhodamine based fluorescent probe for ratiometric sensing of cellular pH

The pH values of lysosomes in cancer cells is slightly lower than that in normal cells, which can be used to distinguish cancer cells from normal cells. According to this, a naphthalimide-rhodamine based fluorescent probe(hereafter referred to as RBN) with a pK_a of 4.20 was designed and synthesized for ratiometric sensing of cellular pH via fluorescence resonance energy transfer(FRET), which can respond to different pH precisely through ratiometric fluorescence intensity(Ⅰ_(577)/Ⅰ_(540)). RBN can be employed to distinguish cancer cells from normal cells on the basis of different fluorescent response, in particular, RBN showed excellent water solubility and low cell toxicity, all these are quite significant for potential application in cancer diagnose and therapy.     

Chromogenic silica nanoparticles for the colorimetric sensing of long-chain carboxylates

Silica nanoparticles functionalized with chromogenic spirobenzopyran and thiourea subunits show selective colour changes in the presence of certain long-chain carboxylates.     

Bio-friendly synthesis of ZnO nanoparticles in aqueous solution at near-neutral pH and low temperature

ZnO nanoparticles are synthesized using a new bio-friendly method. The experimental conditions are very mild: aqueous solution at near-neutral pH and 37 degrees C. The as-obtained nanoparticles show the stable wurtzite structure without the need of annealing. The two reagents used are aqueous solutions of zinc nitrate and buffer tris(hydroxymethyl)aminomethane. This is a standard nontoxic buffer and inert to a wide variety of chemicals and biomolecules, therefore extremely satisfactory for biochemical reactions. Furthermore, this is a polydentade ligand which adsorbs strongly on one or more surfaces of ZnO inhibiting its crystal growth and yielding nearly spherical ZnO nanoparticles. Our objective is to use the crystallization method described here for further incorporation of biomolecules as additives in the reaction solution, aiming at the formation of ZnO with new physical properties.