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    Efficacy of sugar excipients on lyophilized C22 phage infectivity evaluated by atomic force microscopy
    (2022-07-01)
    Manbua, Nathida
    ;
    Suteewong, Teeraporn
    ;
    Sae-Ueng, Udom
    Bacteriophages (phages) show immense potential as biological control agents of pathogenic bacteria in crops. However, their utilization is hindered by the challenges in storage and handling in remote farming areas. Lyophilization has been used to convert phages from solution to powdery form to overcome such issues. In this work, we lyophilized the C22 phage, a promising biocontrol agent of Ralstonia solanacearum causing wilt disease. Sugar excipients were added during the lyophilization step to preserve phage infectivity. We found that 0.5 M sucrose, 0.25 M, and 0.5 M trehalose could retain infectivity of lyophilized C22 phage for ≥ 45% after 90–day storage. Using atomic force microscopy-based imaging, we revealed that both sugars induced aggregation of C22 phage particles. We suggest that aggregation may be a mechanism that prevents phage from degradation since it reduces overall surface that can unfavorably interact with external damaging factors. An insight into phage aggregation can be essential for phage storage and utilization in biocontrol applications.
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    Gold nanorods enhanced resonance Rayleigh scattering for detection of Hg2+ by in-situ mixing with single-stranded DNA
    (2018-02-01)
    Ngernpimai, Sawinee
    ;
    Matulakun, Piyaporn
    ;
    Teerasong, Saowapak
    ;
    Puangmali, Theerapong
    ;
    Kopwitthaya, Atcha
    A resonance Rayleigh scattering (RRS) method for determination of Hg<sup>2+</sup> concentration using positively charged gold nanorods (GNRs) and thymine-rich single-stranded DNA (ssDNA) was developed. Hg<sup>2+</sup> can induce a conformation change of ssDNA from a random coil to a hairpin structure via thymine–Hg<sup>2+</sup>–thymine coordination. Hairpin shaped DNA possesses a high density of negative charges, therefore it caused in a drastic aggregation of GNRs. This resulted in an enhancement of RRS intensity. In this work, a change in RRS intensity proportional to the concentration of Hg<sup>2+</sup> was monitored by spectrofluorometer at excitation and RRS wavelengths of 550 nm (λ<inf>ex</inf> = λ<inf>RRS</inf>). This method offered a detection limit of 0.23 nM, which is lower than the maximum mercury contaminant level specified by the US Environmental Protection Agency. Good precision of analysis was obtained (3.1% relative standard deviation). Furthermore, the method was simple, involving in-situ mixing and sensing in a one-pot solution. Detection was accomplished in 5 min. This makes the method advantageous in terms of convenience and rapidity of analysis. The developed method was successfully applied for detection of Hg<sup>2+</sup> in tap water samples. Recoveries were found in range of 100.6–119.0%.
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