Subpicomolar Sensing of δ-Opioid Receptor Ligands by Molecular-Imprinted Polymers Using Plasmon-Waveguide Resonance Spectroscopy

Plasmon Waveguide Resonance: Principles, Applications and Historical Perspectives on Instrument Development

Plasmon waveguide resonance (PWR) is a variant of surface plasmon resonance (SPR) that was invented about two decades ago at the University of Arizona. In addition to the characterization of the kinetics and affinity of molecular interactions, PWR possesses several advantages relative to SPR, namely, the ability to monitor both mass and structural changes. PWR allows anisotropy information to be obtained and is ideal for the investigation of molecular interactions occurring in anisotropic-oriented thin films. In this review, we will revisit main PWR applications, aiming at characterizing molecular interactions occurring (1) at lipid membranes deposited in the sensor and (2) in chemically modified sensors. Among the most widely used applications is the investigation of G-protein coupled receptor (GPCR) ligand activation and the study of the lipid environment’s impact on this process. Pioneering PWR studies on GPCRs were carried out thanks to the strong and effective collaboration between two laboratories in the University of Arizona leaded by Dr. Gordon Tollin and Dr. Victor J. Hruby. This review provides an overview of the main applications of PWR and provides a historical perspective on the development of instruments since the first prototype and continuous technological improvements to ongoing and future developments, aiming at broadening the information obtained and expanding the application portfolio.

Molecular Imprinted Polymers Coupled to Photonic Structures in Biosensors: The State of Art

Optical sensing, taking advantage of the variety of available optical structures, is a rapidly expanding area. Over recent years, whispering gallery mode resonators, photonic crystals, optical waveguides, optical fibers and surface plasmon resonance have been exploited to devise different optical sensing configurations. In the present review, we report on the state of the art of optical sensing devices based on the aforementioned optical structures and on synthetic receptors prepared by means of the molecular imprinting technology. Molecularly imprinted polymers (MIPs) are polymeric receptors, cheap and robust, with high affinity and selectivity, prepared by a template assisted synthesis. The state of the art of the MIP functionalized optical structures is critically discussed, highlighting the key progresses that enabled the achievement of improved sensing performances, the merits and the limits both in MIP synthetic strategies and in MIP coupling.

Deformable molecularly imprinted nanogels permit sensitivity-gain in plasmonic sensing

Soft molecularly imprinted nanogels (nanoMIPs), selective for human transferrin (HTR), were prepared via a template assisted synthesis. Owing to their soft matter, the nanoMIPs were observed to deform at binding to HTR: while no relevant changes were observed in the hydrodynamic sizes of HTR-free compared to HTR-loaded nanoMIPs, the HTR binding resulted in a significant increment of the nanoMIP stiffness, with the mean Young's modulus measured by AFM passing from 17 ± 6 kPa to 56 ± 18 kPa. When coupled to a plastic optical fibre (POF) plasmonic platform, the analyte-induced nanoMIP-deformations amplified the resonance shift, enabling to attain ultra-low sensitivities (LOD = 1.2 fM; linear dynamic range of concentrations from 1.2 fM to 1.8 pM). Therefore, soft molecularly imprinted nanogels that obey to analyte-induced deformation stand as a novel class of sensitivity-gain structures for plasmonic sensing.

Molecular Imprinting Applications in Forensic Science

Producing molecular imprinting-based materials has received increasing attention due to recognition selectivity, stability, cast effectiveness, and ease of production in various forms for a wide range of applications. The molecular imprinting technique has a variety of applications in the areas of the food industry, environmental monitoring, and medicine for diverse purposes like sample pretreatment, sensing, and separation/purification. A versatile usage, stability and recognition capabilities also make them perfect candidates for use in forensic sciences. Forensic science is a demanding area and there is a growing interest in molecularly imprinted polymers (MIPs) in this field. In this review, recent molecular imprinting applications in the related areas of forensic sciences are discussed while considering the literature of last two decades. Not only direct forensic applications but also studies of possible forensic value were taken into account like illicit drugs, banned sport drugs, effective toxins and chemical warfare agents in a review of over 100 articles. The literature was classified according to targets, material shapes, production strategies, detection method, and instrumentation. We aimed to summarize the current applications of MIPs in forensic science and put forth a projection of their potential uses as promising alternatives for benchmark competitors.

Molecular imprinting science and technology: a survey of the literature for the years 2004-2011

Herein, we present a survey of the literature covering the development of molecular imprinting science and technology over the years 2004-2011. In total, 3779 references to the original papers, reviews, edited volumes and monographs from this period are included, along with recently identified uncited materials from prior to 2004, which were omitted in the first instalment of this series covering the years 1930-2003. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by sections describing fundamental aspects of molecular imprinting including the development of novel polymer formats. Thereafter, literature describing efforts to apply these polymeric materials to a range of application areas is presented. Current trends and areas of rapid development are discussed.

Optical biosensors for food quality and safety assurance-a review

Food quality and safety is a scientific discipline describing handling, preparation and storage of food in ways that prevent food borne illness. Food serves as a growth medium for microorganisms that can be pathogenic or cause food spoilage. Therefore, it is imperative to have stringent laws and standards for the preparation, packaging and transportation of food. The conventional methods for detection of food contamination based on culturing, colony counting, chromatography and immunoassay are tedious and time consuming while biosensors have overcome some of these disadvantages. There is growing interest in biosensors due to high specificity, convenience and quick response. Optical biosensors show greater potential for the detection of pathogens, pesticide and drug residues, hygiene monitoring, heavy metals and other toxic substances in the food to check whether it is safe for consumption or not. This review focuses on optical biosensors, the recent developments in the associated instrumentation with emphasis on fiber optic and surface plasmon resonance (SPR) based biosensors for detecting a range of analytes in food samples, the major advantages and challenges associated with optical biosensors. It also briefly covers the different methods employed for the immobilization of bio-molecules used in developing biosensors.

A molecular-imprint nanosensor for ultrasensitive detection of proteins

Molecular imprinting is a technique for preparing polymer scaffolds that function as synthetic receptors. Imprinted polymers that can selectively bind organic compounds have proven useful in sensor development. Although creating synthetic molecular-imprinting polymers that recognize proteins remains challenging, nanodevices and nanomaterials show promise in this area. Here, we show that arrays of carbon-nanotube tips with an imprinted non-conducting polymer coating can recognize proteins with subpicogram per litre sensitivity using electrochemical impedance spectroscopy. We have developed molecular-imprinting sensors specific for human ferritin and human papillomavirus derived E7 protein. The molecular-imprinting-based nanosensor can also discriminate between Ca(2+)-induced conformational changes in calmodulin. This ultrasensitive, label-free electrochemical detection of proteins offers an alternative to biosensors based on biomolecule recognition.

Peptide-imprinted polymer microspheres prepared by precipitation polymerization using a single bi-functional monomer

A single bi-functional monomer, N,O-bismethacryloyl ethanolamine (NOBE), was used in precipitation polymerization system to synthesize molecularly imprinted polymer (MIP) microspheres. Highly specific binding sites were obtained for N-terminal protected neuropeptides, Boc-Leu-enkephalin and Pyr-Leu-enkephalin. The use of NOBE allowed binding sites to be formed in polymer microspheres that are able to recognize target peptides through the consensus C-terminal sequence. The interesting molecular binding results suggest a new approach for peptide analysis combining in situ chemical modification with MIP recognition under non-aqueous conditions.

Synthesis and chemical stability of a disulfide bond in a model cyclic pentapeptide: cyclo(1,4)-Cys-Gly-Phe-Cys-Gly-OH

Many cyclic peptides are formed using a disulfide bond to increase their conformational rigidity; this provides receptor selectivity and increased potency. However, degradation of the disulfide bond in formulation can lead to a loss of structural stability and biological activity of the peptide. Therefore, the objective of this study was to study the stability of peptide 1 (cyclo(1,4)-Cys-Gly-Phe-Cys-Gly-OH). This cyclic peptide was synthesized using Boc strategy via solution-phase peptide synthesis and purified using semi-preparative HPLC. The accelerated stability studies of the cyclic peptide were conducted in buffer solutions at pH 1.0-11.0 with controlled ionic strengths at 70 degrees C. The pH-rate profile shows that the peptide has an optimal stability around pH 3.0 with a V-shape between pH 1.0 and 5.0. Two small plateaus are observed at pH 5.0-7.0 and pH 8.0-10.0, indicating hydrolysis on different ionized forms of the cyclic peptide. One product was observed at acidic pH due to peptide bond hydrolysis at Gly2-Phe3. The number of degradation products increases as the pH increases from neutral to basic, and most of the degradation products at neutral and basic pH are derived from the degradation at the disulfide bond.