Md. Shahinul Islam

Chemiluminescence detection of label-free C-reactive protein based on catalytic activity of gold nanoparticles.

A novel, quantitative analytical method for measuring C-reactive protein (CRP) levels in human serum has been developed based on the catalytic activity of gold nanoparticles (GNPs) and luminol-H(2)O(2) chemiluminescence (CL). The CL intensity in the presence of CRP and its ligand, O-phosphorylethanolamine (PEA), was greatly enhanced due to the aggregation of GNPs after the addition of 0.5M NaCl. Any pretreatment steps, such as covalent functionalization of GNPs, addition of antibodies, or labeling of CRP, were not needed for CL detection. The CL enhancement was linearly proportional to CRP concentration in the range of 1.88 fM to 1.925 pM. The detection limit of CRP in serum samples was estimated to be as low as 1.88 fM. The detection sensitivity was increased more than 164 times of magnitude over that of the conventional, enzyme-linked immunosorbent assay (ELISA) method. This proposed GNP-based CL detection method offers the advantages of simplicity, rapidity, and sensitivity.

High sensitive detection of C-reactive protein by total internal reflection fluorescence microscopy on rapidly making nanoarray protein chip

This study investigated a method for the high sensitivity detection and quantification of the C-reactive protein (CRP) in human serum using total internal reflection fluorescence microscopy (TIRFM) on a rapidly made nanoarray protein chip. The nanoarray biotin-probe was patterned onto 3-mercaptopropyl trimethoxysilane-coated cover glass with a spot diameter of approximately 400nm within 1min using a NanoeNabler-based surface patterning tool. The unlabeled CRP molecules were detected in human sera using TIRFM, based on a sandwich fluorescence immunoassay. The linear regression for standard CRP in the range of 50zM-1fM was determined using the equation y=0.437x+84.991 (R=0.9993). This proposed method was approximately 2000 times faster than conventional atomic force microscopy based dip-pen nanolithography in terms of the chip manufacturing process. Additionally this method was 6 x 10(6) times more sensitive than enzyme-linked immunosorbent assay and exhibited a wide dynamic linear range (50zM-1fM).

Metal ion-enriched polyelectrolyte complexes and their utilization in multilayer assembly and catalytic nanocomposite films.

The mixing of Ag ion-doped poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAA) produced Ag ion-doped polyelectrolyte complex particles (PECs) in solution. Positively charged Ag ion-doped PECs (Ag ion PECs) with a spherical shape were deposited alternatively with PAA to form a multilayer assembly. The multilayered film containing Ag ion PECs was reduced to generate a composite nanostructure. Metal nanoparticle (NP)-enriched nanocomposite films were formed by an additional process of the postadsorption of precursors on PECs within the nanocomposite films, which resulted in the enhancement of the catalytic and electrical properties of the composite films. Because the films contain PECs that are responsive to changes in pH and most of the NPs are embedded in the PECs, interesting catalytic properties, which are unexpected in a particle-type catalyst, were observed upon pH changes. As a result of the reversible structural changes of the films and the immobilization of the NPs within the films, the film-type catalysts showed enhanced performance and stability during catalytic reactions under various pH conditions, compared to particle-type catalysts.

Controlled Etching of Internal and External Structures of SiO2 Nanoparticles Using Hydrogen Bond of Polyelectrolytes

We have demonstrated a novel strategy for the synthesis of mesoporous silica nanoparticles (MSNPs) using a surfactant-free method under ambient conditions. By the simple addition of an amine-based polymer (polyethylenimine; PEI) with a high molecular weight to a silica nanoparticle (SNP) solution, two types of MSNPs, including rambutan-like MSNPs (R-MSNPs) and hollow MSNPs (H-MSNPs), were produced. The structural changes of the MSNPs were systematically studied using various reaction conditions (reaction time, molar ratio and molecular weight of PEI, etc.) and were observed using electron microscopic techniques. The formation mechanisms of both MSNPs were carefully investigated using XPS, Raman, and IR spectroscopies. Because the synthesized MSNPs are highly porous materials that contain internal organic/inorganic networks, we investigated the removal/adsorption properties of these MSNPs with respect to pollutants toward possible future use in environmental remediation applications. The H-MSNPs exhibited better environmental remediation capabilities relative to the R-MSNPs because PEI is present between the cobweb-like internal structures of the H-MSNPs, thereby providing a significant number of reaction sites for the adsorption of pollutants. The approach presented here can also be used as a direct method for the preparation of intraconnected networks within the substructures.

Polyelectrolyte-mediated hierarchical mesoporous calcium silicates: a platform for drug delivery carrier with ultrahigh loading capacity and controlled release behavior

We have developed a facile method for the poly(allylamine hydrochloride) (PAH)-assisted synthesis of mesoporous calcium silicate hydrates (PAH-CS) with a large specific surface area (BET = 348.4 m2 g-1) and pore volume (Vp = 1.42 cm3 g-1). Tetraethyl orthosilicate (TEOS) was employed as a silicon source, which was rapidly hydrolyzed and reacted with the amine groups of PAH to form spherical SiO2 nanoparticles (PAH-Si). Subsequently, Ca2+ ions reacted with the silicate anions produced during the dissolution of SiO2 in basic media, leading to the formation of the highly porous 3D networks of PAH-CS that were synthesized only under optimized reaction conditions. The PAH-CS containing an excess of Ca2+ and NH3 + enriched the surfaces with a very high cationic charge (ζ = +65.66 mV)and resulted in an extremely high loading capacity for anionic drugs and proteins. Ibuprofen (IBU) and FITC-labeled bovine albumin (FITC-Albumin) were chosen as a model drug and model protein, respectively, to test the loading and delivery efficiencies of the PAH-CS carriers. The ultrahigh drug loading capacities (DLC) and their release patterns were investigated under controlled pH conditions. Strikingly, the highest DLC reported to date (IBU or FITC-Albumin/carrier (3.35 g or 1 g g-1) was achieved in this work. The PAH-CS had no cytotoxic effect on osteoblast-like MC3T3-E1 cell lines evaluated by the LDH (Lactate dehydrogenase) assay in supernatant medium. Furthermore, the PAH-CS carriers could be entirely transformed to hydroxyapatite after releasing the drug in simulated body fluid (SBF), indicating good bioactivity and biodegradability of the PAH-CS carriers.

Free-standing polymer nanoactuators, nanoshutters, and nanofilters

Our study demonstrates a facile approach for the synthesis of metal NP-embedded freestanding polyelectrolyte complexes (PECs) without sacrificial templates, which can be used as nanoactuators, nanoshutters, and nanofilters. The metal NP-PECs were prepared by mixing metal precursor-preadsorbed cation and anion PEs, using a nonstoichiometric ratio, followed by a controlled heat treatment. The metal NP-PECs showed reversible structural changes such as shrinking or swelling when they were exposed to various pH conditions. During the changes, they were also able to reversibly control the interparticle distance of the metal NPs embedded in the PECs, which has allowed the easy tuning of their catalytic and optical properties. By the reversible control of structural changes, the PECs can also be used as nanoshutters to reversibly control the flow of nanomaterials in the channels or pores. Furthermore, metal NP-embedded PECs, Au/Ag-PECs, were demonstrated to be useful as nanofilters for removing or transforming unwanted materials.

Molecular switching fluorescence based high sensitive detection of label-free C-reactive protein on biochip

A novel detection technique on biochip for the quantification of label-free C-reactive protein (CRP) based on molecular switching of fluorescence (MSF) is demonstrated by total internal reflection fluorescence microscopy. It alters fluorescence intensity of fluoreseinamine isomer 1 (FAI) upon binding with its specific ligand, O-phosphorylethanolamine (PEA). In the MSF-based detection, FAI was used as an ink, printed on a 3-glycidoxypropyl-trimethoxysilane (GPTS)-coated glass coverslip. With the addition of GPTS conjugated PEA solution to the FAI-printed coverslip, the fluorescence intensity was remarkably decreased. Addition of CRP increased fluorescence intensity linearly in the range of 800 aM to 500 fM (R=0.997). The MSF-based biochip assay for the estimation of CRP in human sera showed ∼200 times increased detection sensitivity in less than a third of the time to obtain results using a conventional enzyme-linked immunosorbent assay. This biochip detection is a promising new technique for the quantification of CRP molecules from trace amounts of clinical samples.

Self-assembly of individual polymer chain–metal nanoparticles for polymer cargo nanocomposites with tunable properties

We report a simple synthetic method and the unique properties of four types of individual NPs that are well-dispersed in polyelectrolyte complexes (PECs) from the core to the shell without the formation of alloy or core–shell NPs. Additionally, this result cannot be achieved by conventional methods. By mixing and heating PEs with metal precursors, individual metal NPs stabilized by PEs were synthesized. The four types of individual metal NP-containing PECs were prepared by mixing anionic and cationic PEs involving individual metal NPs. The individual metal NPs were homogeneously distributed within the polymer particles, and their contents were easily tuned by varying the loading fractions of the individual metal NP-containing PEs. The as-obtained PEC–Au/Pt/Ag/Pd (separate entities) exhibited promising performance for surface enhanced Raman scattering (SERS) and catalytic activities, which was further enhanced when the four types of metals demonstrated different optimal composition in comparison to the mixed types, such as the alloy or core–shell NPs. Our results also show that it is necessary to tune the types or individual metal contents of the multi-metallic complexes (individual, alloy, or core–shell) for the control or application of certain properties.

Neuron-like polyelectrolyte–carbon nanotube composites for ultra-high loading of metal nanoparticles

We report a simple protocol for the fabrication of multiwalled carbon nanotubes (MWCNTs) with a neuron-like structure for loading ultra-high densities of metal nanoparticles (NPs). The MWCNTs were initially coated with an anionic polyelectrolyte (PE), polystyrene sodium sulfonate (PSS), using a noncovalent interaction (CNT/PSS). The neuron-like structures were fabricated through the stepwise assembly of both the positively charged poly(allylamine) hydrochloride (PAH) and negatively charged poly(acrylic acid) (PAA) in a nonstoichiometric ratio on the CNT/PSS as a template. After three coatings with the PEs, the obtained neuron-shaped CNTs were used as a support for loading a high density of multi-metallic NPs. Moreover, a unique characteristic, tunable and side specific growth of the metal NPs, was also observed. Our neuron-like structures with high loadings of multi-metallic NPs were demonstrated to be catalytic materials for the conversion of 4-nitrophenol to 4-aminophenol and as convenient surface-enhanced Raman scattering substrates for biological tags and molecular detection.