Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing

This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60 nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (～10 nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives-a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pK(a) value of 6.8. The fluorescence intensity of the reference dye did not change significantly (～3.0%) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% of horse serum, indicating that there are no significant statistical differences at a 95% confidence level.     

Ratiometric fluorescence detection of mercury ions in water by conjugated polymer nanoparticles

We present dye-doped polymer nanoparticles that are able to detect mercury in aqueous solution at parts per billion levels via fluorescence resonance energy transfer (FRET). The nanoparticles are prepared by reprecipitation of highly fluorescent conjugated polymers in water and are stable in aqueous suspension. They are doped with rhodamine spirolactam dyes that are nonfluorescent until they encounter mercury ions, which promote an irreversible reaction that converts the dyes to fluorescent rhodamines. The rhodamine dyes act as FRET acceptors for the fluorescent nanoparticles, and the ratio of nanoparticle-to-rhodamine fluorescence intensities functions as a ratiometric fluorescence chemodosimeter for mercury. The light harvesting capability of the conjugated polymer nanoparticles enhances the fluorescence intensity of the rhodamine dyes by a factor of 10, enabling sensitive detection of mercury ions in water at levels as low as 0.7 parts per billion.     

On-site low-power sensing nodes for distributed monitoring of heavy metal ions in water

Heavy metal pollution in water environments poses a great threat to public health and to the ecological environment due to its high toxicity and non-degradability.However,many existing detection methods require laboratory-based bulky instruments and time-consuming manual operations.Although some on-site systems exist,they are difficult to deploy on a large scale owing to their large size and high cost.Here,we report a sensing node featuring low power consumption and low cost,achieved by integrating microsensor,microfluidic,and electronic modules into a compact size for automatic and scalable heavy metal pollution monitoring.Digital microfluidic and electrochemical sensing modules are integrated on a chip,thereby combining the procedures of sample pretreatment,electrochemical sensing,and waste removal for automatic and continuous monitoring.The feasibility of the platform is demonstrated by Pb2+detection in tap water.With a 3500 mA??h battery,the compact sensing node could work for several years in principle.There is scope for further improvements to the system in terms of wider functionality and reductions in size,power consumption,and cost.The sensing node presented here is a strong candidate for distributed monitoring of water quality as an Internet-of-Things application.     

Recent developments and patents on biological sensing using nanoparticles in microfluidic systems

Microfluidic systems provide a total solution of biological and chemical analysis from the sample application to the display of the analysis results. A lot of developments on the point-of-care diagnostic applications have been reported and the commercial possibility is shown. To achieve sensitive and specific biological sensing, nanoparticles may provide a promising tool because they have similar length scale with the biomolecules. The nano-sensing technology suggests a molecular level detection of the biomolecules to pursue higher performance. In this review, recent developments and patents on the biological sensing using nanoparticles in microfluidic systems are discussed. An updated, systematic and rapid reference in the field of nano-biological sensing is provided.     

Optically tunable fluorescent carbon nanoparticles and their application in fluorometric sensing of copper ions

Nano Research - A series of carbon nanoparticles (CNPs) with emission wavelength ranging from 483 to 525 nm were prepared by hydrothermal treatment of poly-3-thiopheneacetic acid (PTA) and NaOH....     

Colorimetric method for determining Pb2+ ions in water enhanced with non-precious-metal nanoparticles

Sulfur anions and their derivatives have long been recognized for their high selectivity and reactivity toward Pb(2+) ions and formation of highly absorptive yet water-insoluble compounds with both acid and base media. This phenomenon has been used for qualitative analysis of lead ions in water. We demonstrate a new method to quantitatively determine the Pb(2+) concentration in the range of 0.5-500 ppm in water using colorimetric measurement, based on forming "soluble" lead sulfide in water enhanced with non-precious-metal nanoparticles. This method has inherent high selectivity for lead over other alkali-metal and alkaline-earth-metal ions. The colorimetric measurements of the absorptive solutions provide accurate determination of the lead concentration in water comparable to that measured using inductively coupled plasma mass spectrometry. To our knowledge, this is the simplest, lowest cost, and easiest-to-use method for detecting and determining the lead concentration in water.     

Noise-free dual-wavelength difference imaging of plasmonic resonant nanoparticles in living cells

Herein, we demonstrated a new optical microscopy method to selectively image small-size gold nanoparticles (GNPs) inside noisy living cells through determination of the difference image between the probe beam (illuminated at the resonance wavelength of GNPs, 532 nm) and the reference beam (illuminated at 473 nm). From computer simulation and single-particle imaging experiments, we demonstrated that GNPs with a diameter of 45 nm could be selectively imaged in the GNPs/cell lysates mixture and inside living cells by dual-wavelength difference (DWD) imaging. The diffusion dynamics of nucleic acids functionalized GNPs on cell membranes and the internalization kinetics of these GNPs by living cells were explored with this method. Our real-time tracking experiments showed that statistically 80% of GNPs were under restricted diffusion on the cell membrane. The cell cytoskeleton fence effect, as observed in the single-particle tracking experiments, may be one of the main factors for the restricted diffusion mode.     

Economical, green synthesis of fluorescent carbon nanoparticles and their use as probes for sensitive and selective detection of mercury(II) ions

The present article reports on a simple, economical, and green preparative strategy toward water-soluble, fluorescent carbon nanoparticles (CPs) with a quantum yield of approximately 6.9% by hydrothermal process using low cost wastes of pomelo peel as a carbon source for the first time. We further explore the use of such CPs as probes for a fluorescent Hg(2+) detection application, which is based on Hg(2+)-induced fluorescence quenching of CPs. This sensing system exhibits excellent sensitivity and selectivity toward Hg(2+), and a detection limit as low as 0.23 nM is achieved. The practical use of this system for Hg(2+) determination in lake water samples is also demonstrated successfully.     

Microdevices for separation, accumulation, and analysis of biological micro- and nanoparticles

Microfabrication and performance of a novel microsystem for separation, accumulation and analysis of biological micro- and nanoparticles is reported. Versatile chip functions based on dielectrophoresis and microfluidics were integrated to isolate particles from complex sample solutions such as serum. A bead-based assay for virus detection is proposed. Separation of micro- and sub-mum beads employing dielectrophoretic deflector and bandpass structures is demonstrated. Individual antibody coated beads with hepatitis A virus bound to their surface were trapped by negative dielectrophoresis in a field cage and analysed by fluorescence microscopy.     

A simple and cost-effective sensing strategy of mercury (II) based on analyte-inhibited aggregation of gold nanoparticles

A simple, cheap and ultrasensitive colorimetric Hg2+ sensing strategy has been developed in this paper. It was based on a special 'Hg2+-inhibited aggregation' mechanism, in which the pyridine-induced aggregation of unmodified gold nanoparticles (AuNPs) could be inhibited upon addition of Hg2+. Compared with the previous Hg2+-induced aggregation mechanism, the new design just employed a cheap and facile chemical reagent, pyridine, as an inducer of aggregation of AuNPs and elimination of the modifying or labeling step. The effects of pyridine concentration and size of AuNPs were investigated. The calibration curve showed that the extinction ratio value at 525 and 700 nm increased linearly over the Hg2+ concentration range of 0.15-3.00 μM with a detection limit of 55 nM. The specificity of this sensor is remarkably high over that of the other metal ions without adding any masking agent.     

Synthesis,characterization, electrical and sensing properties of ZnO nanoparticles

The present study investigates the electrical and sensing properties of mechanically compacted pellets of nanosized zinc oxide powders synthesized by chemical method at room temperature in alcohol base using Triethanolamine (TEA) as capping agent. Synthesized ZnO particles has been characterized for its optical, structural, morphological properties using UV–VIS spectrophotometer, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The ZnO particles have hexagonal wurtzite structure and the particles are of 20–30 nm in size. The electrical properties of the prepared material have been investigated with Impedance Spectroscopy at different temperatures and frequencies and other laboratory setup. Resistivity, I–V curves, AC impedance of ZnO nanoparticles pellets with temperature was investigated and response was compared with commercial ZnO. Piezoelectric and oxygen sensing property of ZnO were also examined. Dynamic hysteresis of sintered ZnO pellet using axis ACCT TF analyzer 2000HS did not show polarization retention by sample. Oxygen sensing of ZnO pellet has been investigated for different concentrations of oxygen for the temperature range of 200–350 °C. The decrease of the current flow through the ZnO pellet with increasing oxygen concentration indicates the application of ZnO in oxygen sensing. The prepared ZnO particles were also used for preparing nanofluids of different concentrations and were characterized by measuring thermal conductivity using hot wire method which shows sigmoidal behavior over a temperature range of 10–50 °C.     

HPLC-ICP-MS法测定水样中的甲基汞、乙基汞和无机汞

建立了高效液相色谱(HPLC)和电感耦合等离子体质谱(ICP-MS)联用测定环境水样中的甲基汞、乙基汞和无机汞的方法。实验使用的高效液相色谱流动相为含有0.06mol/L乙酸氨,20μg/LBi,0.1%(V/V)2-巯基乙醇的5%(V/V)甲醇-水溶液,色谱柱为C18反相柱(5μm,2.1mm×50mm),经前处理的水样在液相色谱中分离后,进入电感耦合等离子体质谱检测其甲基汞、乙基汞和无机汞的浓度。甲基汞、乙基汞和无机汞检出限分别为0.05μg/L、0.10μg/L和0.10μg/L。     

Nucleobase,nucleoside,nucleotide,and oligonucleotide coordinated metal ions for sensing and biomedicine applications

Metal ions play critical roles in chemical,biological,and environmental processes.Various biomolecules have the ability to coordinate with metal ions and form various materials.Nucleobases,nucleosides,and nucleotides,as the essential components of DNA,have emerged as a useful building block for the construction of functional nanomaterials.In recent years,DNA oligonucleotides have also been used for this purpose.We herein review the strategies for the synthesis of soft nanomaterials through the assembly of nucleotides(or DNA)and metal ions to yield various nanoparticles,fibers,and hydrogels.Such coordination methods are simple to operate and can be carried out under ambient conditions.The luminescent,catalytic,and molecular recognition properties of these coordination materials are described with representative recent examples.Their applications ranging from biosensing,enzyme encapsulation,catalysis,templated shell growth to cancer therapy are highlighted.Finally,challenges of this field and future perspectives are discussed.     

Polypyrrole‐modified magnetic nanoparticles and high‐performance liquid chromatography for determination of glibenclamide from biological fluids

In this research, the successful application of polypyrrole (PPy)‐modified magnetic nanoparticles (NPs) is described as an efficient adsorbent for the extraction and the preconcentration of glibenclamide (GB). To measure it in biological fluids samples, HPLC‐UV detection was used. First, iron oxide NPs were prepared by coprecipitation procedure and then their surface was modified by PPy monomers. Characteristics of Fe₃ O₄ @PPy NPs were investigated by FTIR technique and NP size studied with scanning electron microscopy. The vibrating sample magnetometer was used to characterise the magnetic properties of the prepared modified NPs. The affecting parameters in extraction including analyte sorption time, analyte desorption time, ionic strength, sample volume, pH, eluent type, eluent amount, and amount of Fe₃ O₄ @PPy NPs were investigated and optimised. The linear range of the proposed method is 0.2–700.0 μg l⁻¹ and the limit of detection is 0.1 μg l ^{− 1}. The relative standard deviation for five replicate analyses was 3.9. Finally, the proposed procedure was successfully employed for preconcentration and determination of GB in biological fluids.Inspec keywords: nanofabrication, pH, nanomagnetics, desorption, iron compounds, chromatography, adsorption, spectrochemical analysis, nanoparticles, magnetic particles, scanning electron microscopy, Fourier transform infrared spectraOther keywords: polypyrrole‐modified magnetic nanoparticles, high‐performance liquid chromatography, glibenclamide, preconcentration, biological fluids samples, HPLC‐UV detection, iron oxide NPs, coprecipitation procedure, PPy monomers, scanning electron microscopy, vibrating sample magnetometer, magnetic properties, analyte desorption time, analyte sorption time, biological fluids     

Flower-shaped gold nanoparticles: synthesis, characterization and their application as SERS-active tags inside living cells

The detection of Raman signals inside living cells is a topic of great interest in the study of cell biology mechanisms and for diagnostic and therapeutic applications. This work presents the synthesis and characterization of flower-shaped gold nanoparticles and demonstrates their applicability as SERS-active tags for cellular spectral detection. The particles were synthesized by a facile, rapid new route that uses ascorbic acid as a reducing agent of gold salt. Two triarylmethane dyes which are widely used as biological stains, namely malachite green oxalate and basic fuchsin, were used as Raman-active molecules and the polymer mPEG-SH as capping material. The as-prepared SERS-active nanoparticles were tested on a human retinal pigment epithelial cell line and found to present a low level of cytotoxicity and high chemical stability together with SERS sensitivity down to picomolar particle concentrations.     

Synthesis of water soluble quantum dots for monitoring carrier-DNA nanoparticles in plant cells

Fluorescent quantum dots (QDs) have shown great promise for use as biolabels in cell and animal biology and more recently in plant sciences. An important use of QDs is for monitoring the dynamics, intracellular trafficking, and fate of carrier-DNA nanocomplexes in cell transfection and potentially in plant transformation. In this study, a low cost aqueous procedure has been developed to efficiently prepare biocompatible QDs for monitoring nanoparticle-mediated gene transfer in conjunction with molecular breeding of Jatropha curcas. Water-soluble CdSe nanoparticles were synthesized by self-assembly using L-Cysteine as stabilizer and optimal synthesis scheme established by fluorescence spectroscopy. The QDs were used to label chitosan-DNA nanoparticles via electrostatic interaction and the resultant QD-labeled chitosan-DNA complexes were shown to have superior fluorescence properties with red shift of emission and absorption spectra relative to the CdSe QDs alone. This system is being explored as a superior alternative to Agrobacterium-mediated genetic transformation of Jatropha curcas cells. PCR amplification of the full length of the carried reporter gene (GFP) suggests that the DNA was not digested in Jatropha curcas cells transfected with CdSe/CS-DNA complexes. Furthermore, GFP gene expression in the transfected callus cells, as evidenced by fluorescence detection, suggests that the target DNA was integrated into the plant genome.     

A cooperative effect of bifunctionalized nanoparticles on recognition: sensing alkali ions by crown and carboxylate moieties in aqueous media

Reported here is a cooperative effect that the sensing efficiency of the active group on gold nanoparticles (GNPs) can be significantly influenced by another proximal functional group. We previously developed a visual sensing scheme for K+ by 15-crown-5-CH2O(CH2)12SH functionalized GNPs in aqueous matrix. Upon adding K+, the GNP solution changes from red to blue. Such a transform is triggered by a 2-to-1 sandwich complexation of crown to K+, resulting in the red shift of surface plasmon absorption due to GNP aggregation. Herein, we discover that introducing a second functionality, thioctic acid (TA), onto GNPs significantly affects the sensing efficiency of crown moieties (15-crown-5-CH2O(CH2)n)SH and 12-crown-4-CH2O(CH2)nSH, where n = 4, 8, and 12). The rate constant of K+ recognition by TA- and 15-crown-5-CH2O(CH2)4S-bifunctionalized GNPs is more than 4 orders of magnitude faster than the others containing longer methylene chains. The same chain-length dependence is also found in the case of Na+ sensing by 12-crown-4 functionalized GNPs. The discrepancy in sensing performance is attributed to a cooperative effect that the negatively charged carboxylate of TA may preorganize the crown moiety for K+ recognition. This method is applied to measure K+ and Na+ in human urine by UV-visible spectrometry. By adjusting the concentrations of GNPs, the dynamic ranges tuned for K+ and Na+ are, respectively, 6.25 microM-1.12 mM and 0.156-4.00 mM, suitable for real samples pretreated simply by 10-fold dilution. The results ([K+] = 20.3 mM, [Na+] = 45.1 mM) agree with those obtained from ICP-AES ([K+] = 19.8 mM, [Na+] = 43.8 mM).