Jawad Sarfraz

Low-Cost Hydrogen Sulfide Gas Sensor on Paper Substrates: Fabrication and Demonstration

Drop-cast deprotonated emeraldine base (poly)aniline (PANI)-copper chloride films on paper substrates containing ink-jet printed silver electrodes have been prepared and are shown to be promising low-cost gas-sensors for H2S at room temperature. These films showed large changes in the conductivity (three to four orders of magnitude) upon exposure to low concentrations of H2S (10 ppm) due to the formation of CuS and concurrent protonation of PANI. This large response of the sensor can be explained by the relatively large roughness and porosity of this paper substrate. Furthermore, the minimum resistances are low enough to allow light emitting diode lamps to be switched on using a low-voltage battery, thus serving as a proof-of-concept for mass-produced H2S-sensors for, for example, the food packaging industry.

Application of Paper-Supported Printed Gold Electrodes for Impedimetric Immunosensor Development

In this article, we report on the formation and mode-of-operation of an affinity biosensor, where alternate layers of biotin/streptavidin/biotinylated-CRP-antigen/anti-CRP antibody are grown on printed gold electrodes on disposable paper-substrates. We have successfully demonstrated and detected the formation of consecutive layers of supra-molecular protein assembly using an electrical (impedimetric) technique. The formation process is also supplemented and verified using conventional surface plasmon resonance (SPR) measurements and surface sensitive characterization techniques, such as X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The article provides a possible biosensor development scheme, where—(1) fabrication of paper substrate (2) synthesis of gold nanoparticle inks (3) inkjet printing of gold electrodes on paper (4) formation of the biorecognition layers on the gold electrodes and (5) electrical (impedimetric) analysis of growth—all are coupled together to form a test-structure for a recyclable and inexpensive point-of-care diagnostic platform.

Modified zeolitic imidazolate framework-8 as solid-phase microextraction Arrow coating for sampling of amines in wastewater and food samples followed by gas chromatography-mass spectrometry.

In this study, a novel solid phase microextration (SPME) Arrow was prepared for the sampling of volatile low molecular weight alkylamines (trimethylamine (TMA) and triethylamine (TEA)) in wastewater, salmon and mushroom samples before gas chromatographic separation with mass spectrometer as detector. Acidified zeolitic imidazolate framework-8 (A-ZIF-8) was utilized as adsorbent and poly(vinyl chloride) (PVC) as the adhesive. The custom SPME Arrow was fabricated via a physical adhesion: (1) ZIF-8 particles were suspended in a mixture of tetrahydrofuran (THF) and PVC to form a homogeneous suspension, (2) a non-coated stainless steel SPME Arrow was dipped in the ZIF-8/PVC suspension for several times to obtain a uniform and thick coating, (3) the pore size of ZIF-8 was modified by headspace exposure to hydrochloric acid in order to increase the extraction efficiency for amines. The effect of ZIF-8 concentration in PVC solution, dipping cycles and aging temperature on extraction efficiency was investigated. In addition, sampling parameters such as NaCl concentration, sample volume, extraction time, potassium hydroxide concentration, desorption temperature and desorption time were optimized. The Arrow-to-Arrow reproducibilities (RSDs) for five ZIF-8 coated Arrows were 15.6% and 13.3% for TMA and TEA, respectively. The extraction with A-ZIF-8/PVC Arrow was highly reproducible for at least 130 cycles without noticeable decrease of performance (RSD<12.5%). Headspace SPME of 7.5mL sample solution with the fabricated ZIF-8 coated Arrow achieved linear ranges of 1-200ngmL-1 for both TMA and TEA. The limit of quantitation (LOQ) was 1ngmL-1 for both TMA and TEA. The method was successfully applied to the determination of TMA and TEA in wastewater, salmon and mushroom samples giving satisfactory selectivity towards the studied amines.

FRET-reporter nanoparticles to monitor redox-induced intracellular delivery of active compounds

Nanoparticle-mediated drug delivery holds great promise for more specific and efficient therapies, mostly due to their high payload and the integration of targeted delivery functions. However, it is typically not possible to monitor the intracellular release of active compounds directly, which hampers the assessment of novel delivery platforms and non-cytotoxic compounds. Herein, we implemented a FRET (fluorescence resonance energy transfer)-reporter system to semi-quantitatively follow the time-course of the intracellular release of a redox-cleavable compound from a nanoparticle delivery platform. We used silica core–shell particles that could be readily modified with a high density of reactive amino groups, and attached fluorescent reporter molecules as model drug cargo. We coupled a FRET-donor fluorophore via a stable covalent bond, while the FRET-acceptor fluorophore was linked via a disulfide-bridge. Therefore, a loss of FRET reported on redox-induced acceptor compound release. These FRET-reporter nanoparticles allowed us to determine both the time course of cellular internalization as well as the intracellular compound release. Our data show that particle internalization is the rate-limiting step, while compound cleavage occurs quickly after internalization. The presented FRET-reporter approach has the advantage to directly monitor the compound cleavage, as compared to indirect read-outs that are based on their cytotoxic action. We therefore propose that our FRET-reporter particles are suitable to monitor intracellularly redox-releasable compounds that are typically not cytotoxic, such as siRNAs.

Sub-ppm electrical detection of hydrogen sulfide gas at room temperature based on printed copper acetate–gold nanoparticle composite films

This paper presents the sub-ppm level electrical detection of H2S gas at room temperature using printed copper acetate–gold nanoparticle composite films. The excellent sensitivity of these films towards H2S can be attributed to the catalytic activity of gold nanoparticles in combination with the plasma oxidation of copper acetate films.

Enhanced protein adsorption and patterning on nanostructured latex-coated paper

Specific interactions of extracellular matrix proteins with cells and their adhesion to the substrate are important for cell growth. A nanopatterned latex-coated paper substrate previously shown to be an excellent substrate for cell adhesion and 2D growth was studied for directed immobilization of proteins. The nanostructured latex surface was formed by short-wavelength IR irradiation of a two-component latex coating consisting of a hydrophilic film-forming styrene butadiene acrylonitrile copolymer and hydrophobic polystyrene particles. The hydrophobic regions of the IR-treated latex coating showed strong adhesion of bovine serum albumin (cell repelling protein), fibronectin (cell adhesive protein) and streptavidin. Opposite to the IR-treated surface, fibronectin and streptavidin had a poor affinity toward the untreated pristine latex coating. Detailed characterization of the physicochemical surface properties of the latex-coated substrates revealed that the observed differences in protein affinity were mainly due to the presence or absence of the protein repelling polar and charged surface groups. The protein adsorption was assisted by hydrophobic (dehydration) interactions.

Combination of magnetic field and surface functionalization for reaching synergistic effects in cellular labeling by magnetic core–shell nanospheres

Aimed at utilizing high-magnetization nanospheres for magnetic field-enhanced cellular labeling, core-shell structured sandwich-like magnetic mesoporous silica nanospheres were developed. While the magnetite cluster core can provide a high magnetic response for overcoming Brownian motion in cell culture media, the layered silica shell facilitates an efficient fluorescent dye labeling. However, the problem of particle aggregation in cell media, which is strongly enhanced under a magnetic field, significantly impeded the uptake by cells, resulting in difficulties in the precise analysis of the degree of particle internalization by fluorescence-based techniques (flow cytometry and confocal microscopy). To overcome this, reflection-based assessment was employed. Further, emphasis was put on utilizing the unique role of surface-hyperbranched polyethylenimine (PEI) in efficient prevention of particle aggregation prior to cell internalization in the presence of an external magnetic field. The interparticle attraction forces originating from magnetic dipole-dipole interactions are hereby balanced by the steric and electrostatic repulsion forces provided by the PEI functionalization, which leads to dispersed nanospheres in cell culture media during the magnetic-field induced cell labeling. As a consequence, PEI functionalization and the presence of the magnetic field synergistically enhanced the efficiency of MRI-fluorescence dual-mode labeling for cellular tracking.

Modulation of the structural properties of mesoporous silica nanoparticles to enhance the T1-weighted MR imaging capability

In this study, we have investigated the contrast enhancement of Gd(iii) incorporated nanoparticle-based contrast agents (CA) by the modulation of the synthesis and structural parameters of the mesoporous silica nanoparticle (MSN) matrix. In the optimisation process, the structure of the MSN matrix, post-synthesis treatment protocols, as well as the source and incorporation routes of paramagnetic gadolinium centers were considered, with the aim to shorten the T1 weighted relaxation time. After preliminary evaluation of the prepared MSNs as nanoparticulate T1/positive contrast agents based on relaxivity, the structure of the MSN matrix was affirmed as the most decisive property to enhance the r1 relaxivity value, alongside the incorporation route of paramagnetic Gd(iii) centers. Based on these findings, the most promising Gd(iii) incorporated MSN-based CA candidate was further evaluated for its cytocompatibility and intensity enhancement by in vitro phantom MR-imaging of labeled cells. Furthermore, pre-labeled tumors grown on a chick embryo chorioallantoic membrane (CAM) were imaged as an in vivo model on a 3T clinical MRI scanner. Our findings show that the optimized MSN-based CA design enables proper access of water to Gd-centers in the selected MSN matrices, and simultaneously decreases the required amount of Gd(iii) content per mass when evaluated against the other MSNs. Consequently, the required Gd amount on a per-dose basis is significantly decreased with regard to clinically used Gd-based CAs for T1-weighted MR imaging.

Protein and bacterial interactions with nanostructured polymer coatings.

Adsorption of proteins and adhesion of bacteria to a surface is affected by chemical and physical interactions. In this study, polymer coatings and their ability to adsorb avidin and Staphylococcus aureus were investigated. The surface chemistry and topography of the polymer coatings was modified by changing the weight ratio of the hydrophobic polystyrene (PS) and the hydrophilic acrylonitrile butadiene styrene (ABS) components in the polymer blend. Avidin adsorbed less to the ABS phase compared with the PS phase. The side-on orientation of avidin on the ABS surface, however, resulted in a higher specific binding of biotinylated bovine serum albumin. Steric effects and hydrophobic protein-surface interactions decreased the activity of avidin on the PS phase. The increased hydrophobicity and roughness of the polymer coatings enhanced the adhesion of S. aureus. The avidin-coated latex surface with 55% relative surface coverage of the PS phase showed anti-microbial behavior.

Low-cost hydrogen sulfide gas sensor on paper substrates; fabrication and demonstration

Drop-casted deprotonated Emeraldine base (poly)aniline (PANI) - copper chloride films on paper substrates containing ink-jet printed silver electrodes have been prepared and are shown to be promising low-cost gas-sensors for H2S at room temperature. These films showed large changes in the conductivity (three to four orders of magnitude) upon exposure to low concentrations of H2S (10ppm) due to the formation of CuS and concurrent protonation of PANI. This large response of the sensor can be explained by the relatively large roughness and porosity of the paper substrate. Furthermore, the minimum resistances are low enough to allow LED lamps to be switched on using a low-voltage battery, thus serving as a proof-of-concept for mass-produced H2S-sensors for, for example, the food packaging industry.