Liquid Crystal-Based Proton Sensitive Glucose Biosensor

Khan, Mashooq,Park, Soo-Young American Chemical Society 2014 ANALYTICAL CHEMISTRY - Vol.86 No.3

<P>A transmission electron microscopy (TEM) grid filled with 4-cyno-4-pentylbiphenyl (5CB) on the octadecyltrichloro silane-coated glass in an aqueous medium was developed to construct a glucose biosensor by coating poly(acrylicacid-b-4-cynobiphenyl-4-oxyundecylacrylate) (PAA-b-LCP) at the aqueous/5CB interface and immobilizing glucose oxidase (GOx) covalently to the PAA chains. The glucose was detected from a homeotropic to planar orientational transition of 5CB by polarized optical microscopy under crossed polarizers. The maximum immobilization density of the GOx, 1.3 molecules/nm<SUP>2</SUP> obtained in this TEM grid cell enabled the detection of glucose at concentrations as low as 0.02 mM with a response time of 10 s. This liquid crystal-based glucose sensor provided a linear response of birefringence of the 5CB to glucose concentrations ranging from 0.05 to 2 mM with a Michaelis–Menten constant (<I>K</I><SUB>m</SUB>) of 0.32 mM. This new and sensitive glucose biosensor has the merits of low production cost and easy detection through the naked eye and might be useful for prescreening the glucose level in the human body.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancham/2014/ancham.2014.86.issue-3/ac402916v/production/images/medium/ac-2013-02916v_0013.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ac402916v'>ACS Electronic Supporting Info</A></P>

Liquid crystal-based glucose biosensor functionalized with mixed PAA and QP4VP brushes

Khan, Mashooq,Park, Soo-Young Elsevier 2015 Biosensors & bioelectronics Vol.68 No.-

<P><B>Abstract</B></P> <P>4-Cyano-4′-pentylbiphenyl (5CB) in a transmission electron microscopy (TEM) grid was developed for glucose detection by coating with a monolayer of mixed polymer brushes using poly(acrylicacid-<I>b</I>-4-cynobiphenyl-4′-oxyundecylacrylate) (PAA-<I>b</I>-LCP) and quaternized poly(4-vinylpyridine-<I>b</I>-4-cynobiphenyl-4′-oxyundecylacrylate) (QP4VP<I>-b-</I>LCP) (LCP stands for liquid crystal polymer) at the 5CB/aqueous interface. The resultant 5CB in TEM grid was functionalized with the PAA and QP4VP brushes, which were strongly anchored by the LCP block. The PAA brush rendered the 5CB/aqueous interface pH-responsive and the QP4VP brush immobilized glucose oxidase (GOx) through electrostatic interactions without the aid of coupling agents. The glucose was detected through a homeotropic-to-planar orientational transition of the 5CB observed through a polarized optical microscope (POM) under crossed polarizers. The optimum immobilization with a 0.78µM GOx solution on the dual-brush-coated TEM grid enabled glucose detection at concentrations higher than 0.5mM with response times shorter than 180s. This TEM grid glucose sensor provided a linear response of birefringence of the 5CB to glucose concentrations ranging from 0.5 to 11mM with a Michaelis–Menten constant (<I>K</I> <SUB>m</SUB>) of 1.67mM. This new and sensitive glucose biosensor has the advantages of low production cost, simple enzyme immobilization, high enzyme sensitivity and stability, and easy detection with POM, and may be useful for prescreening the glucose level in the human body.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The 5CB in a TEM grid was developed for glucose detection by coating with mixed polymer brushes. </LI> <LI> The PAA make the 5CB/aqueous interface pH-responsive and the QP4VP immobilized glucose oxidase. </LI> <LI> The glucose was detected through a dark to bright orientational transition of the 5CB. </LI> <LI> This new TEM grid sensor enables easy detection of glucose in a complex mixture. </LI> </UL> </P>

2P-18 A liquid-crystal-based DNA biosensor for pathogen detection

여동현,( Mashooq Khan ),박수영 한국공업화학회 2017 한국공업화학회 연구논문 초록집 Vol.2017 No.1

A liquid-crystal-filled transmission electron microscopy (TEM) grid cell coated with the cationic surfactant dodecyltrimethylammonium bromide(DTAB), to which a single-stranded deoxyribonucleic acid probe (ssDNA_probe) was adsorbed at the LC/aqueous interface(TEM_DTAB/DNA), was applied for the highly specific detection of target DNA molecules. The DTAB-coated E7 (used LC mixture) in the TEM grid (TEM_DTAB) exhibited a homeotropic orientation, and changed to a planar orientation upon adsorption of the ssDNA_probe. The TEM_DTAB/DNA was then exposed to complementary (target) ssDNA, which resulted in a planar-to-homeotropic configurational change of E7 that could be observed through a polarized optical microscope under crossed polarizers. The optimum adsorption density (2μM) of ssDNAprobe enabled the detection of ≥0.05nM complementary ssDNA. which broaden the applications of LC-based biosensors to pathogen detection.

Polypyrrole Nanocomposite with Water-Dispersible Graphene

조우근,Mashooq Khan,Loon-Seng Tan,정호신,이신희,박수영 한국고분자학회 2017 Macromolecular Research Vol.25 No.4

Scalable water-dispersible graphene (eGPNc) powders were prepared with consecutive chlorosulfonic acid (CSA)/H2O2 and methylmorpholine N-oxide monohydrate (NMMOm) treatments, followed by the common filtering, sonication, and drying processes. The yield of graphene from expanded graphite (EG) powders prepared by the combined CSA/H2O2 and NMMOm treatments (3.0 wt%) was more than five times that from only the NMMOm treatment (0.6 wt%). The produced eGPNc powders had an almost defect-free graphitic structure with good redispersibility in water and an electrical conductivity of 86.9 S/cm from the filtered eGPNc film. The eGPNc film was dispersed at 0.28 mg/mL in water after centrifugation of the 2 mg/mL aqueous solution at 5000 rpm. The aqueous eGPNc solution was utilized as the reaction medium for the in situ polymerization of pyrrole to produce the polypyrrole (PPy)/graphene nanocomposite. The capacitance of PPy measured from cyclic voltammetry (CV) was improved from 122.8 to 278.6 F/g by loading 1 wt% eGPNc onto the nanocomposite. The capacitance of PPy after 1000 CV cycles was improved from 54.0% to 91.0% by loading 3 wt% eGPNc onto the nanocomposite. This improvement in the capacitance and capacitance-stability is due to the in situ formation of PPy in the well-dispersed aqueous graphene solution. Thus, this simple in situ preparation of PPy with eGPNc in water demonstrated the potential for the diverse applications of water-dispersible eGPNc in various water-based systems such as conducting inks, silver wires, and watersoluble conducting polymers (e.g. poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PSS/PEDOT)) for improving their electron conductivity and stability.

Fabrication of temperature- and pH-sensitive liquid-crystal droplets with PNIPAM-b-LCP and SDS coatings by microfluidics

Jung, Yong-Dae,Khan, Mashooq,Park, Soo-Young The Royal Society of Chemistry 2014 Journal of Materials Chemistry B Vol.2 No.30

<P>Dual responsive (temperature and pH) 4-cyano-4′-pentylbiphenyl (5CB) droplets were fabricated by coating with PNIPAM-<I>b</I>-LCP (PNIPAM: poly(<I>N</I>-isopropylacrylamide) and LCP: poly(4-cyanobiphenyl-4′-oxyundecylacrylate)) and sodium dodecyl sulfate (SDS) using a microfluidic method, and were tested for protein detection. The PNIPAM-<I>b</I>-LCP/SDS-functionalized 5CB droplets were effective in detecting proteins in water through a radial-to-bipolar (R-B) orientational change, with detection limits of 0.95, 1.1, 0.12, and 0.07 μM for bovine serum albumin (BSA), lysozyme (LYZ), hemoglobin (Hb), and chymotrypsinogen (ChTg), respectively. The R-B change of the 5CB droplet occurred above the lower critical solution temperature (LCST) of PNIPAM and at pH values below the pI values of the tested proteins, and was reversible by heating/cooling at the LCST of PNIPAM. These sensitive 5CB droplets are simple to prepare, cost-effective, easily detectable, and re-usable (by temperature control) for protein detection. Further, they can be applied to a biosensor after employing the selective units such as aptamers, antibodies, single-stranded DNA, proteins, peptides, and aptamer-binding RNA on the droplet.</P>

Liquid Crystal-Based Biosensors Using a Strong Polyelectrolyte-Containing Block Copolymer, Poly(4-cyanobiphenyl-4'-oxyundecylacrylate)-b-poly(sodium styrene sulfonate)

Muhammad Omer,박수영,Mohammad Tariqul Islam,Mashooq Khan,김영규,이준형,강인규 한국고분자학회 2014 Macromolecular Research Vol.22 No.8

The interface between a nematic liquid crystal phase, 4-cyano-4′-pentylbiphenyl (5CB) and water wasexamined for protein detection by monitoring the formation of a complex between sodium polystyrene sulfonate(PSSNa) and a positively charged biological species on the 5CB in a transmission electron microscopy (TEM) gridcell coated with a strong anionic polyelectrolyte-containing block copolymer, LCP-b-PSSNa (LCP:poly(4-cyanobiphenyl-4′-oxyundecylacrylate)). This block copolymer was successfully synthesized by reversible addition-fragmentationchain transfer polymerization. A monolayer of LCP-b-PSSNa in a Langmuir Blodgett trough (in whichPSSNa and LCP were located in and above water, respectively, in the TEM grid cell) was transferred to the 5CB/water interface in the 5CB-filled TEM grid that was already placed on octadecyltrichlorosilane-coated glass. Modelproteins such as bovine serum albumin (BSA), hemoglobin (Hb), α chymotrypsinogen-A (ChTg), and lysozyme(LYZ) having different isoelectric points (pIs) were tested for non-specific protein detection. When the protein solutionswere injected into the TEM grid cell, the initial homeotropic orientation of 5CB in the TEM grid cell changedto a planar one below the pIs of the proteins due to electrostatic interactions between PSSNa (- charge) and the proteins(+ charge); this did not occur above the pIs of the tested proteins. The minimum concentrations at which thehomeotropic to planar configurational changes (H-P changes) occurred were 0.02, 0.04, 0.04, and 0.08 wt% forBSA, Hb, ChTg, and LYZ, respectively. Therefore, the positively charged biomaterials were visually detected at thePSSNa-coated LC/water interface during an H-P change by using polarized optical microscopy under crossed polarizers. This simple set-up for non-specific biomaterial detection paves a way for the development of efficient andexcellent quality biosensors.