Allen Chang | National Taipei University of Technology (original) (raw)

Papers by Allen Chang

Antibiotics

The overuse of antibiotics has resulted in the emergence of antibiotic resistance, not only in ba... more The overuse of antibiotics has resulted in the emergence of antibiotic resistance, not only in bacteria but also in fungi. Streptomyces are known to produce numerous secondary metabolites including clinically useful antibiotics. In this study, we screened for antibiotic-producing actinobacteria from soils in Taipei and discovered a Streptomyces strain SC26 that displayed antimicrobial activities against Gram-positive bacteria and fungi, but the compounds are heat-labile. Upon UV mutagenesis, a late-sporulation mutant SC263 was isolated with the same antibiotic spectrum but increased in thermostability. The nature of the antibiotic is not clear, but its activity was resistant to proteolytic, nucleolytic and pancreatic digestions, and was retained by the 100 kDa membrane during filtration. To gather more information on SC263, the genome was sequenced, which produced three contigs with a total of 8.2 Mb and was assigned to the species of Streptomyces spororaveus based on the average nu...

Veterinary Sciences

We evaluated Lactobacillus acidophilus (LA) for adjuvant application in animal vaccines. LA parti... more We evaluated Lactobacillus acidophilus (LA) for adjuvant application in animal vaccines. LA particles (LAPs) are made by treating LA with purification processes and high-pressure homogenization (HPH). We found that LAPs treated with HPH with trehalose and emulsifiers had an average particle size of 179 nm, considerably smaller than LAPs without additives. First, we evaluated the adjuvanticity of LAPs using a murine model with ovalbumin antigens, revealing that LAPs, especially in a five-fold concentration, could induce a considerable antibody response compared with other current adjuvants. In poultry vaccination tests using inactivated Newcastle disease virus, LAPs alone could induce a similar antibody response compared to commercial water-in-oil (W/O) adjuvant ISA70, a commercial adjuvant, at weeks 4 and 6; however, they declined faster than ISA70 at weeks 8 and 10. LAPs added to conventional adjuvant materials, such as mineral oil-based O/W emulsions, showed similar adjuvanticity ...

Sensors and Actuators B: Chemical, 2021

Abstract Electrode poisoning and interferences from complex biological environments are major cha... more Abstract Electrode poisoning and interferences from complex biological environments are major challenges in the development of in-situ H2S sensors. To circumvent these issues, herein a robust electrode based on reduced graphene oxide-molybdenum disulfide nanohybrid (RGO-MoS2) and polymerized o-phenylenediamine (POPD) is developed. The POPD/RGO-MoS2-modified electrode catalyzed H2S oxidation at a minimized overpotential (+ 0.15 V vs. Ag/AgCl). A new strategy based on inherent material properties was implemented to alleviate the electrode-poisoning problem. The nano-tailored interface blocks 2.5-fold surplus levels of interferences because of its exclusive size-exclusion property and electrostatic interactions. Moreover, this method with a response time of fewer than 5 s displayed a detection limit of 10 nM, which covers the endogenous H2S levels. Practicality tests in various biological media yielded valuable recoveries of 96.4–97.8%. The amounts of H2S released from the bacterial cells were quantified in real-time over a continuous time span of 5 h.

Analytical Chemistry, 2018

A first-of-a-kind latent electrochemical redox probe, ferrocene carbamate phenyl acrylate (FCPA),... more A first-of-a-kind latent electrochemical redox probe, ferrocene carbamate phenyl acrylate (FCPA), was developed for the selective detection of cysteine (Cys) and aminoacylase (ACY-1). The electrochemical signal generated by this probe was shown to be highly specific to Cys and insensitive to other amino acids and biological redox reactants. The FCPA-incorporated electrochemical sensor exhibited a broad dynamic range of 0.25-100 µM towards Cys. This probe also proficiently monitored the aminoacylase (ACY-1)-catalyzed biochemical transformation of N-acetylcysteine (NAC) into Cys, and this proficiency was used to develop an electrochemical assay for quantifying active ACY-1, which it did so in a dynamic range of 10-200 pM (0.1-2 mU/cc) with a detection limit of 1 pM (0.01 mU/cc). Furthermore, the probe was utilized in realtime tracking and quantification of cellular Cys production, specifically in E. Coli W3110, along with a whole blood assay to determine levels of Cys and spiked ACY-1 in blood with a reliable analytical performance.

Biosensors and Bioelectronics, 2017

Hydrogen sulfide (H 2 S) was discovered as a third gasotransmitter in biological systems and rece... more Hydrogen sulfide (H 2 S) was discovered as a third gasotransmitter in biological systems and recent years have seen a growing interest to understand its physiological and pathological functions. However, one major limiting factor is the lack of robust sensors to quantitatively track its production in real-time. We described a facile electrochemical assay based on latent redox probe approach for highly specific and sensitive quantification in living cells. Two chemical probes, Azido Benzyl ferrocene carbamate (ABFC) and N-alkyl Azido Benzyl ferrocene carbamate (NABFC) composed of azide trigger group were designed. H 2 S molecules specifically triggered the release of reporters from probes and the current response was monitored using graphene oxide film modified electrode as transducer. The detection limits are 0.32 µM (ABFC) and 0.076 µM (NABFC) which are comparable to those of current sensitive methods. The probes are successful in the determination of H 2 S spiked in whole human blood, fetal bovine serum, and E. coli. The continuous monitoring and quantification of endogenous H 2 S production in E. coli were successfully accomplished. This work lays first step stone towards real-time electrochemical quantification of endogenous H 2 S in living cells, thus hold great promise in the analytical aspects of H 2 S.

Analytica Chimica Acta, 2017

An electrochemical latent redox probe, SAF 5 was designed, synthesized and characterized. A rapid... more An electrochemical latent redox probe, SAF 5 was designed, synthesized and characterized. A rapid and sensitive solution-based assay was demonstrated for salicylate hydroxylase (SHL). In presence of NADH at aerobic conditions, SHL catalyzed the decarboxylative hydroxylation of SAF and released a redox reporter amino ferrocene (AF 6). The release of AF 6 was monitored at interference free potential region (-50 mV vs. Ag|AgCl) using differential pulse voltammetry as signal read-out. The current signal generated by this process is highly specific, and insensitive to other biological interfering compounds. Next, the SAF incorporated SHL assay was extended to fabricate immobilization-free biosensors for rapid sensing of salicylic acid (SA) and β-hydroxybutyrate (β-HB) in whole blood. The described method rapidly detects SA in a linear range of 35-560 µM with detection limit of 5.0 µM. For β-HB determination, the linear range was 10-600 µM and detection limit was 2.0 µM. Besides, the assay protocols are simple, fast, reliable, selective, sensitive and advantageous over existing methods. The whole blood assay did not required cumbersome steps such as, enzyme immobilization, pre-treatments and holds great practical potential in clinical diagnosis.

Sensors and Actuators B: Chemical, 2017