A SCALAR IRRADIANCE FIBER-OPTIC MICROPROBE FOR THE MEASUREMENT OF ULTRAVIOLET RADIATION AT HIGH SPATIAL RESOLUTION

Abstract— The construction of a new type of microprobe for the measurement of scalar irradiance (integral dose rate) in the UV down to wavelengths of 250 nm is described. The microprobes were made from tapered standard optical fibers and a tip-diffuser of magnesia/silica vitroceramic. The sensing tips were ca 100 μm in diameter and had maximal deviations in the angular response of ± 15%. I present measurements of scalar irradiance at high spatial resolution within dry beach sand and suspensions of microorganisms. These two media are environments in which microorganisms are exposed to UV, either under natural (sand) or laboratory conditions (suspensions). In both cases, the space distribution of UV scalar irradiance, and thus the distribution of integral dose rates, departed significantly from that predicted by absorptive effects alone. The results underscore the importance of small-scale, in situ measurements of scalar irradiance for UV dosimetry in such scattering media.     

Preparation of Tip‐Protected Poly(oxyphenylene) Coated Carbon‐Fiber Ultramicroelectrodes

A high‐yield, reliable, and reproducible method has been successfully developed to fabricate poly(oxyphenylene)‐coated carbon fiber ultramicroelectrodes (POCF UMEs) with tip radii r<2 μm. During the insulation process, the tip of the electrochemically etched electrode is protected by inserting it into an inert polymer while the remainder of the electrode is insulated by electrochemical deposition of a 1–3 μm thick poly(oxyphenylene) film. Optimum conditions for poly(oxyphenylene) deposition are developed and the resulting carbon fiber UMEs showed good cyclic voltammetric behavior even after storage for more than one year. These UMEs were tested for use as amperometric scanning electrochemical microscopy (SECM) tips and successfully imaged Au/Kel‐F and Al/SiC_p metal matrix composites.     

A SERS Optophysiological Probe for the Real‐Time Mapping and Simultaneous Determination of the Carbonate Concentration and pH Value in a Live Mouse Brain

To have a profound understanding of the physiological and pathological processes in a brain, both chemical and electrical signals need to be recorded, but this is still very challenging. Herein, micrometer‐ to nanometer‐sized SERS optophysiological probes were created to determine both the CO₃^2? concentration and the pH in live brains and neurons because both species play important roles in regulating the acid–base balance in the brain. A ratiometric SERS microarray of eight microprobes with tip sizes of 5 μm was established and used for the first time for real‐time mapping and simultaneous quantification of CO₃^2? and pH in a live brain. We found that both the CO₃^2? concentration and the pH value dramatically decreased under ischemic conditions. The present SERS technique can be combined with electrophysiology without cross‐talk to record both electrical and chemical signals in brains. To deepen our understanding of the mechanism of ischemia on the single‐cell level, a SERS nanoprobe with a tip size of 200 nm was developed for use in a single neuron.     

Novel Solid‐Contact Ion‐Selective Microelectrodes for Localized Potentiometric Measurements

The design and properties of novel type of solid‐contact ionophore‐based ion‐selective microelectrodes are reported. The microelectrode is based on an insulated needle‐shaped metallic wire with an exposed apex. The ion‐to‐electron transducer is made of poly(3‐octylthiophene‐2,5‐diyl) and placed between an ion‐selective membrane and the metallic tip. The ion‐selective polyvinyl chloride‐based membrane is deposited atop the layer of conductive polymer. The length of the ion‐sensitive part of the electrode is less than 10 μm. pH and Mg²⁺‐selective microelectrodes were constructed and tested showing stable potential and fast response that are essential properties for the practical application of microelectrodes for localized scanning measurements.     

Comparison of Different Strategies on DNA Chip Fabrication and DNA‐Sensing: Optical and Electrochemical Approaches

New strategies for the construction of DNA chips and the detection of DNA hybridization will be discussed in this review. The focus will be on the use of polypyrrole as a linker between a substrate and oligonucleotide probes. The modification step is based on the electrochemical copolymerization of pyrrole and oligonucleotides bearing a pyrrole group on its 5′ end. This strategy was employed for the immobilization of oligonucleotides on millimeter‐sized electrodes, microelectrode arrays, as well as for the local structuring of homogeneous gold surfaces. Our approaches for the localized patterning of gold surfaces will be also discussed. Localized immobilization was achieved by using an electrospotting technique, where a micropipette served as an electrochemical cell where spot sizes with 800 μm diameters were fabricated. The use of a microcell using a Teflon covered metal needle with a cavity of 100 μm resulted in immobilized probe spots of 300 μm. Scanning electrochemical microscopy (SECM) was also used, and surface modifications of 100 μm were obtained depending on the experimental conditions. Different detection methods were employed for the reading of the hybridization event: fluorescence imaging, surface plasmon resonance imaging (SPRI), photocurrent measurements, and voltamperometric measurements using intercalators. Their advantages concerning the various immobilization strategies will also be discussed.     

Near‐field laser ablation inductively coupled plasma mass spectrometry: a novel elemental analytical technique at the nanometer scale

An analytical technique utilizing a near‐field effect (to enhance the incident light energy on the thin tip of an Ag needle) in a laser ablation inductively coupled plasma mass spectrometry (NF‐LA‐ICP‐MS) procedure was developed. To produce the thin needles with a tip diameter in the hundreds of nm range a robust needle etching procedure was established. The ‘sample‐to‐tip’ distance was controlled via the measurement of a tunnel current between the needle and sample surface. The NF‐LA‐ICP‐MS technique thus developed was applied for the analysis of copper isotopic standard reference material NIST SRM 976 and tungsten‐molybdenum alloy NIST SRM 480 in the nm resolution range. The observed craters ranged from 200 nm to about 2 µm in diameter and were dependent on the needle used as well as on the ‘sample‐to‐tip’ distance. The mass spectrometric measurements of ⁶³Cu⁺ ion intensity on NIST SRM 976 showed that using near‐field enhancement in laser ablation allowed a roughly 6‐fold increase in the ion intensity of the analyte when the needle was about 100 nm (and below) from the surface, in contrast to when it was far away (e.g. 10 µm) from the sample. The relative standard deviation (RSD) of the ⁶⁵Cu⁺/⁶³Cu⁺ isotopic ratio measurements by NF‐LA‐ICP‐MS was 3.9% (n = 9). The detection efficiencies obtained for the compared LA‐ICP‐MS and NF‐LA‐ICP‐MS methods were found to be 4.6 * 10^?3 counts per second (cps)/ablated atom and 2.7 * 10^?5 cps/ablated atom, respectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of new poly(ethyleneimine)‐g‐poly(methyl methacrylate) star‐block copolymers with hyperbranched cationic core

Hyperbranched polyethyleneimine (hb‐PEI) is used as polymeric scaffold to synthesize new PEI‐g‐polymethylmethacrylate (PEI‐g‐PMMA) block copolymers, consisting of a hyperbranched, partially quarternized cationic core, and PMMA‐arms. The arms are grafted to the PEI scaffold by means of the “grafting to” method. Ammonium groups, covalently bond to the hyperbranched core, provide good adhesion to negatively charged surfaces, even in case of low‐surface charges. The PMMA strands provide compatibility of the macromolecules to PMMA matrices, hence generating potential dispersants, and compatibilizers for PMMA. A peculiar association behavior in organic solution is observed as supported by dynamic light scattering and DOSY measurements. First evidences of the applicability of the macromolecules as dispersants to prepare PMMA‐nanocomposites are given. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3700–3715     

Light‐induced self‐thermophoresis of Janus spheroidal nanoparticles

A theoretical framework is provided for determining the self‐thermophoretic velocity of a light irradiated spheroidal Janus nanoparticle consisting of symmetric dielectric and perfectly conducting semi‐spheroids. The analysis is based on solving the linearized Joule heating problem due to uniform laser irradiance and on explicitly determining the temperature fields inside and outside the particle. We employ the thermoelectric (Peltier‐ Seebeck) methodology to find the surface self ‐ induced temperature gradient and the related slip velocity which determines the autonomous phoretic (self ‐ propulsion) mobility of the Janus particle. Simplified explicit expressions for the self ‐ thermophoretic velocities of spheroidal (prolate and oblate) Janus particles in terms of their aspect ratios are found and few practical limiting cases (i.e., sphere, disk and needle) are also discussed.     

Nonlinear optical side‐chain polymers post‐functionalized with high‐β chromophores exhibiting large electro‐optic property

Electro‐optic side‐chain polymers have been synthesized by the post‐functionalization of methacrylate isocyanate polymers with novel phenyl vinylene thiophene vinylene bridge (FTC) nonlinear optical chromophores. For this application, FTC‐based chromophores were modified in their electronic donor structure, exhibiting much larger molecular hyperpolarizabilities compared with the benchmark FTC. Of these new chromophores, absorption spectra, hyper‐Rayleigh scattering experiment, and thermal analysis were carried out to confirm availability as effective nonlinear optical units for electro‐optic side‐chain polymers. The electro‐optic coefficients (r₃₃) of obtained polymers were investigated in the process of in situ poling by monitoring the temperature, current flow, poling field, and electro‐optic signal. Compared with the nonsubstituted analogue, benxyloxy modified FTC chromophore significantly achieved higher nonlinear optical property, exhibiting molecular hyperpolarizability at 1.9 μm of 4600 × 10^?30 esu and an r₃₃ value of 150 pm/V at the wavelength of 1.31 μm. Synthesized electro‐optic polymers showed high glass transition temperature (T_g), so that the temporal stability examination exhibited >78% of the electro‐optic intensity remaining at 85 °C over 500 h. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A Small‐Molecule Two‐Photon Probe for Nitric Oxide in Living Tissues

Two‐photon microscopy (TPM) has become an indispensable tool in the study of biology and medicine due to the capability of this method for molecular imaging deep inside intact tissues. For the maximum utilization of TPM, a variety of two‐photon (TP) probes for specific applications are needed. In this article, we report a small‐molecule TP probe (ANO1) for nitric oxide (NO) that shows a rapid and specific NO response, a 68‐fold fluorescence enhancement in response to NO, and a maximum TP‐action cross‐section of 170 GM (GM: 10^?50 cm⁴ photon^?1) upon reaction with excess NO. This probe can be easily loaded into cells and tissues and can real‐time monitor NO in living tissues at 100–180 μm depth for longer than 1200 s through the use of TPM, with minimum interference from other biologically relevant species.     

Mapping alternating current electroosmotic flow at the dielectrophoresis crossover frequency of a colloidal probe

AC electroosmotic (ACEO) flow above the gap between coplanar electrodes is mapped by the measurement of Stokes forces on an optically trapped polystyrene colloidal particle. E²‐dependent forces on the probe particle are selected by amplitude modulation (AM) of the ACEO electric field (E) and lock‐in detection at twice the AM frequency. E²‐dependent DEP of the probe is eliminated by driving the ACEO at the probe's DEP crossover frequency. The location‐independent DEP crossover frequency is determined, in a separate experiment, as the limiting frequency of zero horizontal force as the probe is moved toward the midpoint between the electrodes. The ACEO velocity field, uncoupled from probe DEP effects, was mapped in the region 1–9 μm above a 28 μm gap between the electrodes. By use of variously sized probes, each at its DEP crossover frequency, the frequency dependence of the ACEO flow was determined at a point 3 μm above the electrode gap and 4 μm from an electrode tip. At this location the ACEO flow was maximal at ～117 kHz for a low salt solution. This optical trapping method, by eliminating DEP forces on the probe, provides unambiguous mapping of the ACEO velocity field.     

Pt Nanoparticle‐modified Carbon Fiber Microelectrode for Selective Electrochemical Sensing of Hydrogen Peroxide

We report a simple approach to the production of carbon fiber‐based amperometric microbiosensors for selective detection of hydrogen peroxide (H₂O₂), which was achieved by electrometallization of carbon fiber microelectrodes (CFMs) by electrodeposition of Pt nanoparticles. The Pt‐carbon hybrid sensing interface provided a sensitivity of 7711±587 μA ? mM^?1 ? cm^?2, a detection limit of 0.53±0.16 μM (S/N=3), a linear range of 0.8 μM–8.6 mM, and a response time of <2 sec. The morphologies of the Pt nanoparticle‐modified CFMs were characterized by scanning electron microscopy. To achieve selectivity, permseletive layers, polyphenylenediamine (PPD) and Nafion, were deposited resulting in exclusion of the anionic and cationic interferents, ascorbic acid and dopamine, respectively, at their physiologically relevant concentrations. The resultant sensors displayed a sensitivity to hydrogen peroxide of 1381±72 μA ? mM^?1 ? cm^?2, and a detection limit of 0.86±0.19 μM (S/N=3). This simple and rapid metallization method converts carbon fiber microelectrodes, which are readily accessible, to microscale Pt electrodes in 2 min, providing a platform for oxidase‐based amperometric biosensors with improved spatial resolution over more commonly used platinum electrode array microprobes.     

SERS活性光纤光谱微探针研究

用真空蒸镀银岛膜和银溶胶自组装膜两种方法对光纤探针进行表面增强拉曼(SERS)活性修饰,构造了圆锥型SERS活性光纤光谱微探针.选取几个有代表性的分子作为检测样品,得到了低浓度样品的SERS光谱,对样品BVPP的检测下限达到10^-9mol/L.比较两种修饰光纤探针的检测结果可知,银溶胶自组装膜修饰更有优势.     

Inhibiting sorbent stripping by designing a sorbent‐packed porous probe for headspace solid‐phase microextraction

To prevent the stripping of coating sorbents in headspace solid‐phase microextraction, a porous extraction probe with packed sorbent was introduced by using a porous stainless steel needle tube and homemade sol–gel sorbents. The traditional stainless‐steel needle tube was punched by a laser to obtain two rows of holes, which supply a passageway for analyte vapor during extraction and desorption. The sorbent was prepared by a traditional sol–gel method with both poly(ethylene glycol) and hydroxy‐terminated silicone oil as coating ingredients. Eight polycyclic aromatic hydrocarbons and six benzene series compounds were used as illustrative semi‐volatile and volatile organic compounds in sequence to verify the extraction performance of this porous headspace solid‐phase microextraction probe. It was found that the analysis method combining a headspace solid‐phase microextraction probe and gas chromatography with mass spectrometry yielded determination coefficients of no less than 0.985 and relative standard deviations of 4.3–12.4%. The porous headspace solid‐phase microextraction probe showed no decrease of extraction ability after 200 uses. These results demonstrate that the packed extraction probe with porous structure can be used for headspace solid‐phase microextraction. This novel design may overcome both the stripping and breakage problems of the conventional coating fiber.     

Aligning poly[1,6‐di‐(N‐carbazolyl)‐2,4‐hexadiyne] crystalline fibers as conducting channels for transistor applications

Aligned crystallites of 1,6‐di‐(N‐carbazolyl)‐2,4‐hexadiyne (DCHD) were prepared on the phenyltrichlorosilane‐modified SiO₂/Si surface using the brush‐coating method. The length and width as well as the orientation of the crystallites depend on the coating speed. At a lower coating speed of 0.2 ~ 0.3 mm/s, well‐separated fibers with a width of 1–2 μm and a length of hundreds of μm were grown along the coating direction. Higher speeds resulted in shorter fibers together with randomly oriented tiny crystallites appearing in between. The diacetylene crystallites upon UV irradiation gave polydiacetylene fibers with deformations along the fiber axis. The poly(ene‐yne) backbones were shown to align along the fiber axes. With these poly‐DCHD fibers as a conducting channel for transistor fabrication, a highest field‐effect mobility of 0.039 cm²/Vs was obtained.     

Multifunctional Nitrogen‐Doped Carbon Nanodots for Photoluminescence,Sensor, and Visible‐Light‐Induced H2 Production

Herein, multifunctional N‐doped carbon nanodots (NCNDs) were prepared through the one‐step hydrothermal treatment of yeast. Results show that the NCNDs can be used as a new photocatalyst to drive the water‐splitting reaction under UV light. Moreover, the NCNDs can efficiently catalyze the hydrogen evolution reaction. Under visible‐light irradiation, Eosin Y‐sensitized NCNDs exhibit excellent activity for hydrogen evolution. The hydrogen evolution rate of NCNDs (without any modification and co‐catalyst) reaches 107.1 μmol h^?1 (2142 μmol g^?1 h^?1). When Pt is loaded on the NCNDs, the hydrogen evolution rate reaches 491.2 μmol h^?1 (9824 μmol g^?1 h^?1) under visible‐light irradiation. In addition, the NCNDs show excellent fluorescent properties and can be applied as a fluorescent probe for the sensitive and selective detection of Fe³⁺.     

Preparation and application of a coated‐fiber needle extraction device

In this study, a needle‐trap device with fibers coated with a molecularly imprinted polymer was developed for separation. A number of heat‐resistant Zylon filaments were longitudinally packed into a glass capillary, followed by coating with a molecularly imprinted polymer. Then, the molecularly imprinted polymer coating was copolymerized and anchored onto the surface of the fibers. The bundle of synthetic fibers coated with the molecularly imprinted polymer was packed into a 21G stainless‐steel needle and served as an extraction medium. The coated‐fiber needle extraction device was used to extract volatile organic compounds from paints and gasoline effectively. Subsequently, the extracted volatile organic compounds were analyzed by gas chromatography. Calibration curves of gaseous benzene, toluene, ethylbenzene, and o‐xylene in the concentration range of 1–250 μg/L were obtained to evaluate the method, acceptable linearity was attended with correlation coefficients above 0.998. The limit of detection of benzene, toluene, ethylbenzene, and o‐xylene was 11–20 ng/L using the coated‐fiber needle‐trap device. The relative standard deviation of needle‐to‐needle repeatability was less than 8% with an extraction time of 20 min. The loss rates after storage for 3 and 7 days at room temperature were less than 30%.     

A multi-mode fiber probe for holographic micromanipulation and microscopy

Holographic tweezers have revolutionized the way we do experiments at the micron scale. The possibility of applying controlled force fields on simultaneously trapped micro-particles has allowed to directly probe interactions and mechanical properties of colloids, macromolecules and living cells. Holographic micromanipulation requires the careful shaping of a laser beam that is then focused by a microscope objective onto a micro-hologram in the sample volume. The same objective is used for imaging. That approach is therefore limited to in vitro samples contained in transparent cells that are easily accessed optically. Here we demonstrate that the complex light propagator of a real multimode fiber can be directly measured. That allows to transmit a micro-hologram through a 1 metre long (60 μm core) optical fiber and produce dynamic arrays of focused spots at the fiber output. We show that those spots can be used for interactive holographic micromanipulation of micron sized beads facing the fiber tip. Scanning a single spot across the output fiber we can employ the same fiber as a probe for scanning fluorescence microscopy. Our findings open the way towards the fabrication of endoscopic probes which could be capable of seeing and manipulating single cells deep into biological tissues.     

Fabrication of boronate‐decorated polyhedral oligomeric silsesquioxanes grafted cotton fiber for the selective enrichment of nucleosides in urine

Various cotton fiber based boronate‐affinity adsorbents are recently developed for the sample pretreatment of cis‐diol‐containing biomolecules, but most do not have efficient capacity due to limited binding sites on the surface of cotton fibers. To increase the density of boronate groups on the surface of cotton fiber, polyhedral oligomeric silsesquioxanes were used to modify cotton fiber to provide plentiful reactive sites for subsequent functionalization with 4‐formylphenylboronic acid. The new adsorbent showed special recognition ability towards cis‐diols and high adsorption capacity (175 μg/g for catechol, 250 μg/g for dopamine, 400 μg/g for adenosine). The in‐pipette‐tip solid‐phase extraction was investigated under different conditions, including pH and ionic strength of solution, adsorbent amount, pipette times, washing solvent, and elution solvent. The in‐pipette‐tip solid‐phase extraction coupled with high‐performance liquid chromatography was used to analyze four nucleosides in urine samples. Under the optimal extraction conditions, the detection limits were determined to be between 5.1 and 6.1 ng/mL (S/N  =  3), and the linearity ranged from 20 to 500 ng/mL for these analytes. The accuracy of the analytical method was examined by studying the relative recoveries of analytes in real urine samples with recoveries varying from 83 to 104% (RSD = 3.9–10.2%, n = 3).     

Quasi‐simultaneous Mapping of Local Current Density,pH and Dissolved O2

For the first time we report on quasi‐simultaneous mapping of local current density, pH and concentration of dissolved O₂. The three micro‐probes were positioned 50 micron apart from each other and 50 to 100 µm above the cut‐edge metal coated steel sample. The vibrating probe recorded the local current density and glass‐capillary micro‐electrode measured local pH. Additionally, two different micro‐probes were used for DO measurements: either an amperometric micro‐probe or micro‐optode was coupled with the other two sensors using the triple head stage. The data on local distributions were acquired quasi‐simultaneously (within ≤ 2.8 s) and, hence, are correlated in space and time.