Caleb Acquah

A review on immobilised aptamers for high throughput biomolecular detection and screening.

The discovery of Systematic Evolution of Ligands by Exponential Enrichment (SELEX) assay has led to the generation of aptamers from libraries of nucleic acids. Concomitantly, aptamer-target recognition and its potential biomedical applications have become a major research endeavour. Aptamers possess unique properties that make them superior biological receptors to antibodies with a plethora of target molecules. Some specific areas of opportunities explored for aptamer-target interactions include biochemical analysis, cell signalling and targeting, biomolecular purification processes, pathogen detection and, clinical diagnosis and therapy. Most of these potential applications rely on the effective immobilisation of aptamers on support systems to probe target species. Hence, recent research focus is geared towards immobilising aptamers as oligosorbents for biodetection and bioscreening. This article seeks to review advances in immobilised aptameric binding with associated successful milestones and respective limitations. A proposal for high throughput bioscreening using continuous polymeric adsorbents is also presented.

Development and characteristics of polymer monoliths for advanced LC bioscreening applications: A review

Biomedical research advances over the past two decades in bioseparation science and engineering have led to the development of new adsorbent systems called monoliths, mostly as stationary supports for liquid chromatography (LC) applications. They are acknowledged to offer better mass transfer hydrodynamics than their particulate counterparts. Also, their architectural and morphological traits can be tailored in situ to meet the hydrodynamic size of molecules which include proteins, pDNA, cells and viral targets. This has enabled their development for a plethora of enhanced bioscreening applications including biosensing, biomolecular purification, concentration and separation, achieved through the introduction of specific functional moieties or ligands (such as triethylamine, N,N-dimethyl-N-dodecylamine, antibodies, enzymes and aptamers) into the molecular architecture of monoliths. Notwithstanding, the application of monoliths presents major material and bioprocess challenges. The relationship between in-process polymerisation characteristics and the physicochemical properties of monolith is critical to optimise chromatographic performance. There is also a need to develop theoretical models for non-invasive analyses and predictions. This review article therefore discusses in-process analytical conditions, functionalisation chemistries and ligands relevant to establish the characteristics of monoliths in order to facilitate a wide range of enhanced bioscreening applications. It gives emphasis to the development of functional polymethacrylate monoliths for microfluidic and preparative scale bio-applications.

SELEX Modifications and Bioanalytical Techniques for Aptamer–Target Binding Characterization

ABSTRACT The quest to improve the detection of biomolecules and cells in health and life sciences has led to the discovery and characterization of various affinity bioprobes. Libraries of synthetic oligonucleotides (ssDNA/ssRNA) with randomized sequences are employed during Systematic Evolution of Ligands by Exponential Enrichment (SELEX) to select highly specific affinity probes called aptamers. With much focus on the generation of aptamers for a variety of target molecules, conventional SELEX protocols have been modified to develop new and improved SELEX protocols yielding highly specific and stable aptamers. Various techniques have been used to analyze the binding interactions between aptamers and their cognate molecules with associated merits and limitations. This article comprehensively reviews research advancements in the generation of aptamers, analyses physicochemical conditions affecting their binding characteristics to cellular and biomolecular targets, and discusses various field applications of aptameric binding. Biophysical techniques employed in the characterization of the molecular and binding features of aptamers to their cognate targets are also discussed.

Deploying aptameric sensing technology for rapid pandemic monitoring

Abstract The genome of virulent strains may possess the ability to mutate by means of antigenic shift and/or antigenic drift as well as being resistant to antibiotics with time. The outbreak and spread of these virulent diseases including avian influenza (H1N1), severe acute respiratory syndrome (SARS-Corona virus), cholera (Vibrio cholera), tuberculosis (Mycobacterium tuberculosis), Ebola hemorrhagic fever (Ebola Virus) and AIDS (HIV-1) necessitate urgent attention to develop diagnostic protocols and assays for rapid detection and screening. Rapid and accurate detection of first cases with certainty will contribute significantly in preventing disease transmission and escalation to pandemic levels. As a result, there is a need to develop technologies that can meet the heavy demand of an all-embedded, inexpensive, specific and fast biosensing for the detection and screening of pathogens in active or latent forms to offer quick diagnosis and early treatments in order to avoid disease aggravation and unnecessary late treatment costs. Nucleic acid aptamers are short, single-stranded RNA or DNA sequences that can selectively bind to specific cellular and biomolecular targets. Aptamers, as new-age bioaffinity probes, have the necessary biophysical characteristics for improved pathogen detection. This article seeks to review global pandemic situations in relation to advances in pathogen detection systems. It particularly discusses aptameric biosensing and establishes application opportunities for effective pandemic monitoring. Insights into the application of continuous polymeric supports as the synthetic base for aptamer coupling to provide the needed convective mass transport for rapid screening is also presented.

Prospects in the use of aptamers for characterizing the structure and stability of bioactive proteins and peptides in food

AbstractFood-derived bioactive proteins and peptides have gained acceptance among researchers, food manufacturers and consumers as health-enhancing functional food components that also serve as natural alternatives for disease prevention and/or management. Bioactivity in food proteins and peptides is determined by their conformations and binding characteristics, which in turn depend on their primary and secondary structures. To maintain their bioactivities, the molecular integrity of bioactive peptides must remain intact, and this warrants the study of peptide form and structure, ideally with robust, highly specific and sensitive techniques. Short single-stranded nucleic acids (i.e. aptamers) are known to have high affinity for cognate targets such as proteins and peptides. Aptamers can be produced cost-effectively and chemically derivatized to increase their stability and shelf life. Their improved binding characteristics and minimal modification of the target molecular signature suggests their suitability for real-time detection of conformational changes in both proteins and peptides. This review discusses the developmental progress of systematic evolution of ligands by exponential enrichment (SELEX), an iterative technology for generating cost-effective aptamers with low dissociation constants (Kd) for monitoring the form and structure of bioactive proteins and peptides. The review also presents case studies of this technique in monitoring the structural stability of bioactive peptide formulations to encourage applications in functional foods. The challenges and potential of aptamers in this research field are also discussed. Graphical abstractAdvancing bioactive proteins and peptide functionality via aptameric ligands

Process Analysis of Microalgae Biomass Thermal Disruption for Biofuel Production

The continual usage of petroleum-sourced fuels is now widely recognized as unsustainable due to the depleting supplies, and the contribution of these fuels to the accumulation of greenhouse gases in the environment. A suitable alternative is the utilisation of renewable transport fuels. These fuels are environmentally friendly and economically sustainable. Biodiesel and bioethanol derived from plant lipids and carbohydrate-based crops are potential renewable alternatives to petroleum fuels. In recent years, the cultivation of microalgae as an alternative feedstock for the production of biofuel has received significant attention. This is as a result of the fact that, they have a fast growth rate, can accumulate high quantities of lipids and carbohydrates intracellularly for the production of biodiesel and bioethanol, respectively. That notwithstanding, the processes involved in the cultivation of microalgae, dewatering, biochemical extraction, and conversion to biofuels are energy intensive and as a result undermine its full-scale application potentials. This therefore has necessitated the need for an intensive attention and research in order to debottleneck the aforementioned areas. Electroporation, High pressure homogenization (HPH), Ultrasonic and Bead mills are examples of present cell disruption technologies. However, the electroportation process which at present seems more energy efficient than the rest has only been tried on a lab scale, and yet to be experimented on an industrial scale capacity. In this work, a successful design of an energy-efficient cell disruption technology that can treat up to a mass scale of 10,000 gal/annum of lipids was designed by means of thermal lysis. A comparative analysis with other methods reveals that the designed system is significantly reliable, with the least fractional energy registered as low as 0.41 at an algal concentration of 6 kg/m3.

Chromatographic characterisation of aptamer-modified poly(EDMA-co-GMA) monolithic disk format for protein binding and separation

ABSTRACT The introduction of aptameric ligands onto disk-monolithic adsorbent, representing a unique strategy for convective isolation of target molecules with high specificity and selectivity, is investigated for the first time. Experimental results showed that the disk monolith possessed a good permeability of 1.67 ± 0.05 × 10–14 m2 (RSD = 3.2%). The aptameric ligand density for the aptamer-modified disk monolith was 480 pmol/uL. Chromatographic analysis of the aptamer disk-monolith efficiency showed an optimum linear velocity of 126 cm/min (≈0.25 mL/min) at room temperatures 25 ± 2°C. The theoretical number of plates corresponding to the optimum linear velocity was 128.2 with an height equivalent to the theoretical plate of 0.022 mm. The disk aptamer-immobilised monolithic system demonstrated good selectivity and isolation of thrombin from non-targets.

Protein-Based Nanodelivery Systems for Food Applications

Food-derived proteins are considered ideal materials for the development of encapsulation and delivery system for bioactive ingredients due to their biophysicochemical properties. The size of the protein-delivery systems in the intestinal media is critical in ensuring effective biophysicochemical characteristics such as biorecognition, biocompatibility, bioavailability, bioadhesion and stability. As such, it is important to understand the nature, process and characteristics of different nanoformulations produced with food-derived proteins, together with their drawbacks in food, pharmaceutical and biomedical applications. Current techniques used in the design of protein-based nanodelivery system include nanoemulsificaiton, coacervation, antisolvent precipitation, electrospraying and electrospinning. Brief descriptions of these techniques are presented in this paper, as well as some key characteristics of the resulting nanoparticles. The drawback of individual techniques is also discussed for the consideration of food scientists and biotechnologists who design nanodelivery systems for bioactive ingredients.

Aptameric Sensing in Food Safety

Abstract Foodborne illnesses are a global menace on public health. However, because they are expensive, time-consuming, and nonspecific, standard methods used before now for detecting foodborne pathogens and biotoxins are often unsuitable for real-time detection and surveillance, particularly in low-resource communities that may serve as the source of the food basket in a geographical location. Improvements in systems for the robust detection and screening of foodborne pathogens are therefore needed to effectively regulate the transmission of foodborne pathogens by promoting early treatment and/or isolation of infected products. Interestingly, research work in bioaffinity interactions have led to advances in SELEX (systematic evolution of ligands by exponential enrichment) technology for the generation of short, single-stranded DNA/RNA molecular probes (known as aptamers) that bind selectively to specific pathogenic targets and membrane receptors. Immobilized aptamers also yields aptasensors that are effective for detection in real time. This chapter focuses on the merits and applicability of various established apta-assays over conventional techniques for the detection and screening of foodborne pathogens and biotoxins.

Bioprocessing of Functional Ingredients from Flaxseed

Flaxseeds (Linum usitatissimum L.) are oilseeds endowed with nutritional constituents such as lignans, lipids, proteins, fibre, carbohydrates, and micronutrients. Owing to their established high nutritional profile, flaxseeds have gained an established reputation as a dietary source of high value functional ingredients. Through the application of varied bioprocessing techniques, these essential constituents in flaxseeds can be made bioavailable for different applications such as nutraceuticals, cosmetics, and food industry. However, despite their food and health applications, flaxseeds contain high levels of phytotoxic compounds such as linatine, phytic acids, protease inhibitors, and cyanogenic glycosides. Epidemiological studies have shown that the consumption of these compounds can lead to poor bioavailability of essential nutrients and/or health complications. As such, these components must be removed or inactivated to physiologically undetectable limits to render flaxseeds safe for consumption. Herein, critical description of the types, characteristics, and bioprocessing of functional ingredients in flaxseed is presented.