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Recent development of unconventional aqueous biphasic system: characteristics, mechanisms and applications

Kee PE, Ng TC, Lan JC, Ng HS

Crit Rev Biotechnol, 2020 Jun;40(4):555-569.
PMID: 32283954 DOI: 10.1080/07388551.2020.1747388

Aqueous biphasic system (ABS) is widely used in the recovery, extraction, purification and separation of proteins, enzymes, nucleic acids and antibodies. The ABS with high water content and low interfacial tension offers a biocompatible environment for the recovery of labile biomolecules. Process integration can be achieved using ABS by incorporating multiple-steps of purification, concentration and purification of biomolecules in a single-step operation which often results in high product recovery yield and purity. Conventional ABS is usually formed by aqueous solutions of two polymers or a polymer and a salt above a critical concentration. The high viscosity of polymer-based ABS causes slow phase separation and hinders the mass transfer of biomolecules, whereas polymer/salt ABS is characterized by high ionic strength resulting in the loss of bioactivity of recovered biomolecules. These limitations have encouraged the development of novel ABS which is more cost-effective for various biotechnological applications. This review discusses the characteristics and mechanisms of several types of emerging unconventional ABS using phase-forming components such as hyperbranched polymers, special salts, surfactants, magnetic fields, the addition of nanoparticles and incorporation of various solvent. Moreover, several novel applications of ABS for different separation purposes such as microfluidic-based ABS, ABS bioreactors, application of ABS as an analytical tool, and ABS micropatterning are discussed in this review. In the last section of this review, a comprehensive summary of process integration using ABS for extractive fermentations, bioconversion, crystallization and precipitation is also supplemented for the comprehensive review of various types and applications of ABS in recent years.
Primary purification of intracellular Halomonas salina ectoine using ionic liquids-based aqueous biphasic system

Ng HS, Wan PK, Ng TC, Lan JC

J Biosci Bioeng, 2020 Aug;130(2):200-204.
PMID: 32389469 DOI: 10.1016/j.jbiosc.2020.04.003

Ectoine is a zwitterionic amino acid derivative that can be naturally sourced from halophilic microorganisms. The increasing demands of ectoine in various industries have urged the researches on the cost-effective approaches on production of ectoine. Ionic liquids-based aqueous biphasic system (ILABS) was applied to recover Halomonas salina ectoine from cells hydrolysate. The 1-butyl-3-methylimidazolium tetrafluoroborate (Bmim)BF4 was used in the ILABS and the recovery efficiency of ILABS to recover ectoine from H. salina cells lysate was evaluated by determining the effects of phase composition; pHs; crude loading and additional neutral salt (NaCl). The hydrophilic ectoine was targeted to partition to the hydrophilic salt-rich phase. A total yield (YB) of 96.32% ± 1.08 of ectoine was obtained with ILABS of phase composition of 20% (w/w) (Bmim)BF4 and 30% (w/w) sulfate salts; system pH of 5.5 when the 20% (w/w) of crude feedstock was applied to the ILABS. There was no significant enhancement on the ectoine recovery efficiency using the ILABS when NaCl was added, therefore the ILABS composition without the additional neutral salt was recommended for the primary purification of ectoine. Partition coefficient (KE) of 30.80 ± 0.42, purity (PE) of 95.82% and enrichment factor (Ef) of 1.92 were recorded with the optimum (Bmim)BF4/sulfate ILABS. These findings have provided an insight on the feasibility of recovery of intracellular biomolecules using the green solvent-based aqueous system in one single-step operation.
Partition efficiency of cytochrome c with alcohol/salt aqueous biphasic flotation system

Ng HS, Ng TC, Kee PE, Tan JS, Yim HS, Lan JC

J Biosci Bioeng, 2020 Feb;129(2):237-241.
PMID: 31629635 DOI: 10.1016/j.jbiosc.2019.08.013

Aqueous biphasic flotation (ABF) integrates aqueous biphasic system (ABS) and solvent sublation for recovery of target biomolecules. The feasibility of the alcohol/salt ABF for exclusive partition of cytochrome c to one specific phase of the system was investigated. Aliphatic alcohols of different carbon chain length (ethanol, 1-propanol and 2-propanol) and salts (sulfate, phosphate and citrate) were used for the phase formation. The effects of phase composition, concentration of sample loading, pH, flotation time and flow rate of the system on the partition efficiency of cytochrome c were determined. Cytochrome c was exclusively partitioned to the alcohol-rich top phase of the ABF of 18% (w/w) ethanol and 26% (w/w) ammonium sulfate with pH 6 and 20% (w/w) of sample loading. Highest partition coefficient (K) of 6.85 ± 0.21 and yield (YT) of 99.40% ± 0.02 were obtained with optimum flotation rate of 10 mL/min and flow rate of 10 min.
Factors influencing healthcare seeking in patients with dengue: Systematic review

Ng TC, Teo CH, Toh JY, Dunn AG, Ng CJ, Ang TF, et al.

Trop Med Int Health, 2022 Jan;27(1):13-27.
PMID: 34655508 DOI: 10.1111/tmi.13695

OBJECTIVE: Delays in seeking healthcare for dengue are associated with poor health outcomes. Despite this, the factors influencing such delays remain unclear, rendering interventions to improve healthcare seeking for dengue ineffective. This systematic review aimed to synthesise the factors influencing healthcare seeking of patients with dengue and form a comprehensive framework.
METHODS: This review included both qualitative and quantitative studies. Studies were obtained by searching five databases, contacting field experts and performing backward reference searches. The best-fit meta-synthesis approach was used during data synthesis, where extracted data were fitted into the social-ecological model. Sub-analyses were conducted to identify the commonly reported factors and their level of statistical significance.
RESULTS: Twenty studies were selected for meta-synthesis. Eighteen factors influencing healthcare seeking in dengue were identified and categorised under four domains: individual (11 factors), interpersonal (one factor), organisational (four factors) and community (two factors). The most reported factors were knowledge of dengue, access to healthcare, quality of health service and resource availability. Overall, more barriers to dengue health seeking than facilitators were found. History of dengue infection and having knowledge of dengue were found to be ambiguous as they both facilitated and hindered dengue healthcare seeking. Contrary to common belief, women were less likely to seek help for dengue than men.
CONCLUSIONS: The factors affecting dengue healthcare-seeking behaviour are diverse, can be ambiguous and are found across multiple social-ecological levels. Understanding these complexities is essential for the development of effective interventions to improve dengue healthcare-seeking behaviour.