The development of fluorescent silica nanoparticles (SNP-RB) from natural amorphous silica and its performance as an Escherichia coli (E. coli) biosensor is described in this paper. SNP-RB was derived from silica recovered from geothermal installation precipitation and modified with the dye, Rhodamine B. The Fourier Infrared (FTIR) confirms the incorporation of Rhodamine B in the silica matrix. Transmission Electron Microscopy (TEM) micrographs show that the SNP-RB had an irregular structure with a particle diameter of about 20–30 nm. The maximum fluorescence spectrum of SNP-RB was recorded at 580 nm, which was further applied to observe the detection performance of the fluorescent nanoparticles towards E. coli. The sensing principle was based on the fluorescence-quenching mechanism of SNP-RB and this provided a wide linear E. coli concentration range of 10–10⁵ CFU/mL with a limit detection of 8 CFU/mL. A rapid response time was observed after only 15 min of incubation of SNP-RB with E. coli. The selectivity of the biosensor was demonstrated and showed that the SNP-RB only gave quenching response only to live E. coli bacteria. The use of SNP-RB as a sensing platform reduced the response time significantly compared to conventional 3-day bacterial assays, as well having excellent analytical performance in terms of sensitivity and selectivity.

Butyrolactone I (BL-I) has been reported as inhibitor of α-glucosidase and antioxidant compound isolated from culture broth of Aspergillus terreus. The purpose of this study was to determine the effect of various liquid media compositions on production of BL-I from A. terreus LS07. Fermentation was conducted in four liquid medium: potato dextrose broth (PDB), potato malt peptone (PMP), malt extract (ME), and Czapek-Dox broth (CDB), which were incubated for seven days at room temperature, with agitation of 70 rpm. Ethyl acetate (EtOAc) was used to extract the active metabolite from each broth. Glucosidase inhibitory activity was measured by the inhibition of yeast α-glucosidase, while antioxidants measured by testing the total phenol and DPPH free radical scavenger activity. The results showed that the EtOAc extract on CDB had strong inhibition activity against the enzyme α-glucosidase and strong antioxidant with IC50 values 6.45 and 24.05 μg/mL, respectively. The CDB extract also showed the highest content of total phenols (349.66 mg Gallic Acid Equivalent (GAE)/g extract) and BL-I (58.5% w/w). Based on these results, among the four kinds of medium used, Czapek-Dox broth is an ideal culture medium of A. terreus LS07 that could be applied for increase production of BL-I as natural antidiabetic source from terestrial fungi