Biological Binding Events Research Articles

Magnetic Nanoparticle Mediated Enhancement of Localized Surface Plasmon Resonance for Ultrasensitive Bioanalytical Assay in Human Blood Plasma

We demonstrate that Fe(3)O(4) magnetic nanoparticle (MNP) can greatly enhance the localized surface plasmon resonance (LSPR) of metal nanoparticle. The high refractive index and molecular weight of the Fe(3)O(4) MNPs make them a powerful enhancer for plasmonic response to biological binding events, thereby enabling a significant improvement in the sensitivity, reliability, dynamic range, and calibration linearity for LSPR assay of small molecules in a trace amount. Rather than using fluorescence spectroscopy or magnetic resonance imaging, this study marks the first use of the label-free LSPR nanosensor for a disease biomarker in physiological solutions, providing a low cost, clinical-oriented detection. This facile and ultrasensitive nanosensor with an extremely light, robust, and low-cost instrument is attractive for miniaturization on a lab-on-a-chip system to deliver point-of-care medical diagnostics. To further evaluate the practical application of Fe(3)O(4) MNPs in the enhancement of LSPR assay, cardiac troponin I (cTnI) for myocardial infarction diagnosis was used as a model protein to be detected by a gold nanorod (GNR) bioprobe. MNP-captured cTnI molecules resulted in spectral responses up to 6-fold higher than direct cTnI adsorption on the GNR sensor. The detection limit (LOD) was lowered to ca. 30 pM for plasma samples which is 3 orders lower than a comparable study. To the best of our knowledge, this marks the lowest LOD for a real plasma protein detection based on label-free LSPR shift without complicated instrumentation. The observed LSPR sensing enhancement by Fe(3)O(4) MNPs is independent of nonspecific binding.

Plasmonic Sensing via Photoluminescence of Individual Gold Nanorod

Label-free plasmonic sensors based on localized surface plasmon resonances of nanostructured noble metal materials usually transduce optical refractive index changes occurring in the vicinity of the nanostructures by optical scattering or by extinction. We demonstrate in experiments that the photoluminescence of plasmonic nanoparticles can also be employed to detect biological molecule binding events efficiently. Photoluminescence probably due to plasmon emission of a single gold nanorod presents a similar resonance peak and resembles the response to a refractive index change observed by scattering. The well-known biotin–streptavidin binding assay was detected successfully using the photoluminescence of an individual isolated nanorod. The localized surface plasmon resonances’ responses by scattering in situ with the same nanorod and control experiments were also performed to verify the sensing process. The results evidence that a nanoscale plasmonic sensor can also be archived effectively through the phot...

Microelectrode array biosensor for studying carbohydrate-mediated interactions

Carbohydrate-mediated host-pathogen interactions are essential to bacterial and viral pathogenesis, and represent an attractive target for the development of antiadhesives to prevent infection. We present a versatile microelectrode array-based platform to investigate carbohydrate-mediated protein and bacterial binding, with the objective of developing a generalizable method for screening inhibitors of host-microbe interactions. Microelectrode arrays are well suited for interrogating biological binding events, including proteins and whole-cells, and are amenable to electrochemical derivitization, facilitating rapid deposition of biomolecules. In this study, we achieve microelectrode functionalization with carbohydrates via controlled polymerization of pyrrole to individual microelectrodes, followed by physisorption of neoglycoconjugates to the polypyrrole-coated electrodes. Bioactivity of the immobilized carbohydrates was confirmed with carbohydrate-binding proteins (lectins) detected by both fluorescent and electrochemical means. The platform's ability to analyze whole-cell binding was demonstrated using strains of Escherichia coli and Salmonella enterica, and the dose-dependent inhibition of S. enterica by a soluble carbohydrate antiadhesive.

Detection of human serum albumin on protein array using scanning tunneling microscopy

Electrical detection of biological binding events, such as protein–protein interaction and DNA hybridization, has emerged as an alternative method to conventional colorimetric and fluorescence based methods. In this study, we demonstrate an electrical detection technique of protein array which can be simply extended for multifunctional measurements and detection of biological binding events on micro-scale array. Micro-contact technique was used for the fabrication of protein chip. The fabricated protein array on Au substrate was characterized by fluorescence microscopy and scanning tunneling microscopy (STM). The chip was designed to investigate immunocomplexes comprised of our model protein, human serum albumin (HSA), corresponding antibody fragments, and Au nanoparticle–antibody conjugates. The peak-like pulse obtained by electrical tunneling current between these complexes and the STM tip varies on the surface density of the bound complexes. Using the electrical detection technique based on STM, 100 fg/mL of HSA could be successfully detected by STM. Importantly, the proposed concept of measurement could allow multiple analyses of analytes at nano-scale array, which is difficult to be analyzed by conventional fluorescence based method.

Electrical detection-based analytic biodevice technology

Numerous traditional detection technologies such as fluorescence-based methods and enzymelinked immune-sorbent assay (ELISA) have been evaluated for the measurement of biological binding events. However, conventional detection methods are unsuitable for miniaturization and are unsatisfactory candidates for integration into hand-held sensors. Thus, electrical detection of biological binding events, such as protein-protein interaction and DNA hybridization, has emerged as an alternative method to currently used colorimetric and fluorescence-based methods. Due to its response time, cost effectiveness, high sensitivity, and ease of integration with semiconductor technology, the demand for this technology is increasing. This article reviews electrical detection systems focusing on electrical detection-based nanowire biosensors, protein chip based on electrical detection systems, and cell chip based on electrochemical detection methods.

The matrix neutralized

Many of the best methods available for monitoring biological binding events can't be used in a diverse range of clinical samples. An ultrasensitive assay based on magnetic signals overcomes this problem.

A new approach for bioassays based on frequency- and time-domain measurements of magnetic nanoparticles

We demonstrate a one-step wash-free bioassay measurement system capable of tracking biochemical binding events. Our approach combines the high resolution of frequency- and high speed of time-domain measurements in a single device in combination with a fast one-step bioassay. The one-step nature of our magnetic nanoparticle (MNP) based assay reduces the time between sample extraction and quantitative results while mitigating the risks of contamination related to washing steps. Our method also enables tracking of binding events, providing the possibility of, for example, investigation of how chemical/biological environments affect the rate of a binding process or study of the action of certain drugs. We detect specific biological binding events occurring on the surfaces of fluid-suspended MNPs that modify their magnetic relaxation behavior. Herein, we extrapolate a modest sensitivity to analyte of 100 ng/ml with the present setup using our rapid one-step bioassay. More importantly, we determine the size-distributions of the MNP systems with theoretical fits to our data obtained from the two complementary measurement modalities and demonstrate quantitative agreement between them.

Computational modeling of texture formation and optical performance of liquid crystal films on patterned surfaces

An integrated microstructural‐optical model based on the tensorial Landau–de Gennes liquid crystal theory, the Matrix–Berreman optical model, and the finite‐difference time‐domain (FDTD) optical method is used to investigate texture formation and polarized light propagation in thin nematic liquid crystal (NLC) films for various anchoring boundary conditions mimicking surface conditions of an existing liquid crystal (LC)‐based biosensor device used to detect biological binding events. The integrated mathematical model of the optical device describes the signal generation process of the biosensor based on LC vision. The FDTD optical method predicts two important optical signatures of the transmitted polarized light: oscillations and nonsymmetric optical signals. However, the approximate Matrix–Berreman optical method cannot predict these important optical responses when strong lateral orientation gradients are present. The model predictions are found to be in good agreement with actual experimental results, and can be used to detect interfacial LC orientation due to bound biomolecules.

Modification of Escherichia coli single-stranded DNA binding protein with gold nanoparticles for electrochemical detection of DNA hybridization

The unique binding event between Escherichia coli single-stranded DNA binding protein (SSB) and single-stranded oligonucleotides conjugated to gold (Au) nanoparticles is utilized for the electrochemical detection of DNA hybridization. SSB was attached onto a self-assembled monolayer (SAM) of single-stranded oligonucleotide modified Au nanoparticle, and the resulting Au-tagged SSB was used as the hybridization label. Changes in the Au oxidation signal was monitored upon binding of Au tagged SSB to probe and hybrid on the electrode surface. The amplified oxidation signal of Au nanoparticles provided a detection limit of 2.17 pM target DNA, which can be applied to genetic diagnosis applications. This work presented here has important implications with regard to combining a biological binding event between a protein and DNA with a solid transducer and metal nanoparticles.

Increased sensitivity of surface plasmon resonance of gold nanoshells compared to that of gold solid colloids in response to environmental changes.

Gold nanoshells have been synthesized by reacting aqueous HAuCl4 solutions with solid templates such as silver nanoparticles. The morphology, void space, and wall thickness of these hollow nanostructures were all determined by the templates, which were completely converted into soluble species during the replacement reaction. The surface plasmon peaks of these gold nanoshells were considerably red-shifted as compared to gold solid colloids having approximately the same dimensions. In addition, the surface plasmon resonance of gold nanoshells exhibited a much more sensitive response toward environmental changes even when compared with solid colloids with a mean size much smaller than that of gold nanoshells. For example, the sensitivity factor (i.e., the shift in peak position per unit change in the refractive index of the surrounding medium) was 408.8, 60.0, and 70.9 nm per refractive index unit for gold nanoshells with a mean diameter of 50 nm and wall thickness of 4.5 nm, gold solid colloids of 50 nm in diameter, and gold solid colloids of 30 nm in diameter, respectively. The formation of alkanethiolate self-assembled monolayers on their surfaces caused the plasmon peaks to red-shift by 3.0 nm per methylene unit for gold nanoshells and 0.2 nm per methylene unit for solid colloids with a mean size of 50 nm. Such enhanced sensitivities should make gold nanoshells particularly useful as optical probes for chemical or biological binding events at solid-liquid interfaces.

Conformational analysis of the 1,4-dihydropyridines linking the structural aspects to the biological binding event: a study of the receptor-site conformation

A conformational analysis involving a set of 45 2,6-dimethyl-3,5-dicarbomethoxy-4-X-phenyl-1,4-dihydropyridine derivatives was performed. The potential energy surfaces of the rotation of the phenyl ring around the pyridine ring were constructed for each compound. These were arranged in groups of five in descending order of biological activity. The energy level below 99% of the molecular population for each molecule was superimposed on those groups. The conformationally stable regions permitted to this molecular population were found and compared. The analysis of each group of potential energy surfaces thus constructed revealed that in the biologically active conformation the phenyl ring bisects the pyridine ring and the ortho/meta phenyl substituents are spatially away from the pyridine ring.