Green chemical method was applied to synthesize nanoparticles using recombinant
bromelain. Among the numerous applications of recombinant bromelain, there is still no research
on nanoparticles synthesis which encourages its utilization in this study. Four chemicals which are
copper (II) chloride dihydrate (CuCl2.2H2O), cerium nitrate hexahydrate (Ce(NO3)3.6H2O), sodium
selenite (Na2SeO3), and iron (III) chloride hexahydrate (FeCl3.6H2O) were selected to be screened
for the suitability in nanoparticles biosynthesis by recombinant bromelain. The nanoparticles
formed were characterized by using UV-visible absorption spectra. The biosynthesis process then
was optimized by varying the centrifugation speed, temperature, and time to get the maximum
absorption and weight of nanoparticles through central composite design (CCD) tool. Only
CuCl2.2H2O showed a positive result for the screening process which was represented by the
formation of colloidal solution and a maximum absorption at 580 nm. Thus, optimization was
carried out for this chemical. Based on the optimization model, maximum absorption and weight
were predicted at 67.5°C, 2 hrs, and 9,600 rpm. These optimal conditions were validated by
repeating the biosynthesis process. The absorption and weight of the nanoparticles depended on the
reaction of the chemical with recombinant bromelain. 3D plots showed that the optimal condition
for high responses mostly depends on temperature and time.
Biosensors fabricated with whole-cell bacteria appear to be suitable for detecting bioavailability and toxicity effects of the chemical(s) of concern, but they are usually reported to have drawbacks like long response times (ranging from hours to days), narrow dynamic range and instability during long term storage. Our aim is to fabricate a sensitive whole-cell oxidative stress biosensor which has improved properties that address the mentioned weaknesses. In this paper, we report a novel high-throughput whole-cell biosensor fabricated by immobilizing roGFP2 expressing Escherichia coli cells in a k-carrageenan matrix, for the detection of oxidative stress challenged by metalloid compounds. The E. coli roGFP2 oxidative stress biosensor shows high sensitivity towards arsenite and selenite, with wide linear range and low detection limit (arsenite: 1.0 × 10(-3)-1.0 × 10(1) mg·L(-1), LOD: 2.0 × 10(-4) mg·L(-1); selenite: 1.0 × 10(-5)-1.0 × 10(2) mg·L(-1), LOD: 5.8 × 10(-6) mg·L(-1)), short response times (0-9 min), high stability and reproducibility. This research is expected to provide a new direction in performing high-throughput environmental toxicity screening with living bacterial cells which is capable of measuring the bioavailability and toxicity of environmental stressors in a friction of a second.