Eka Safitri

Ion-selective membrane technology is a key for accurately measuring specific ions in different solutions. A study on Al³⁺ ion selective electrodes (ISEs) based on polyurethane (PU) membranes using an active substance, i.e., 1,10-phenanthroline, was successfully conducted. The results showed the highest sensitivity and linear range with a PU membrane composition of castor oil, toluene diisocyanate, 1,10-phenanthroline, and acetone in the ratio of 37.80 : 18.90 : 43.20 : 0.10 (%w/w) and internal solution composition 0.1 : 0.1 (M) of KCl and Al(NO₃)₃ Fourier transform infrared (FTIR) analysis indicated the presence of urethane bonds at a wavenumber of 3390 cm⁻¹. 1,10-Phenanthroline aromatic CC and C–N functional group peaks appeared at wavenumbers of 1600 cm⁻¹ and 1325 cm⁻¹, respectively. X-ray diffraction (XRD) characterization suggested a decrease in the degree of crystallinity of PU, PU/Phen membranes, and PU/Phen/Al. Scanning electron microscopy (SEM) analysis showed that the PU/Phen/Al membrane had a homogeneous dense outer layer and tended to be porous in the inner layer, and the Al³⁺ ISE system showed an average sensitivity, linear range, and detection limit of 19.94 ± 0.26 mV/decade, 10⁻¹⁰–10⁻⁴ M (R² = 0.998), and 5.17 × 10⁻¹² M, respectively. Furthermore, the ISE had a response time of 180 s, was stable in the pH range of 6–8 and allowed 33 days of use without any interference from foreign ions. The recovery was in the range of 99.21–101.57%. Therefore, the prepared PU/Phen/Al membrane is promising for ISE sensors, especially for the detection of Al³⁺ ions.

A Cr³⁺ ion selective electrode (ISE) based on a polyurethane (PU) membrane from castor oil modified with the active substances 1,10-phenanthroline and graphene was constructed. The ISE consisted of an internal solution with an optimum composition of 0.1 M KCl:Cr(NO₃)₃ and showed a sensitivity of 20.37 ± 0.51 mV decade⁻¹. Spectroscopic analysis showed that urethane bonds were observed at wave number 3390 cm⁻¹ and 1,10-phenanthroline bonds, proven by the aromatic C=C and C–N bonds, respectively at 1600 cm⁻¹ and 1325 cm⁻¹. The modified PU membranes showed a decrease in crystallinity. However, increased crystallinity was observed when the membrane was in a solution of Cr(III) ions. Furthermore, the membrane exhibited a homogeneous solid outer layer structure and a hollow inner layer. The Cr(III) ISE can measure Cr³⁺ ion concentrations in the range of 10⁻¹¹–10^–5 M with coefficient of determination, detection limit, and response time of 0.996, 10^–11 M, and 180 s, respectively. The ISE showed a stable response in the pH range of 5–7. The selectivity of ISE Cr³⁺ towards foreign ions did not interfere with measurements with K _ij values less than 1. In addition, the Cr³⁺ ISE demonstrated good reproducibility and repeatability with an average standard deviation value of less than 5%.

Development of a carbon electrode sensor from used tire waste via pyrolysis, modified with ethylenediaminetetraacetic acid (EDTA) for mercury detection using the cyclic voltammetry (CV) method. EDTA plays a role in metal complexation due to its strong response to mercury metal. The FTIR results of the carbon electrode and EDTA show a C–N bond at a wavenumber of 1,217.08 cm−1, indicating the presence of EDTA. The SEM results reveal a clear difference between the unmodified carbon electrode and the EDTA-modified carbon electrode. The calibration graph is linear, with an R2 value of 0.9961, a sensitivity of 0.3472, as well as LoD and LoQ values of 0.03 and 0.08 ppm, respectively. The correlation coefficient is less than 2%, and the %recovery is within the allowable error range. Mercury measurements in Sungai Mas water samples, Aceh Barat, using voltammetry and AAS, exceed the threshold set by Indonesian Government Regulation (PPRI) No. 22 of 2021. The t-test results for the two Hg measurement methods at a 5% significance level (α) show that tcalculated < ttable (0.083 < 2.571). This indicates no significant difference between the voltammetry and AAS methods for measuring Hg concentrations in water.

This research has successfully fabricated ion selective electrode (ISE) for Pb²⁺ using castor oil (Ricinus communis L.)-based polyurethane (PU) membrane with 1,10-phenanthroline as the active agent. The sensitivity of the Pb²⁺ ISE obtained is 27.25 mV/decade with a linear range of [Pb(NO₃)₂] of 10⁻¹⁰–10⁻⁵ M and a coefficient of determination (R²) of 0.959. The system response reaches stability after 25 s of measurement. The Pb²⁺ has a detection limit of 10⁻¹⁰ M and gives a stable response at pH 7–8 with a 15-day lifetime. The investigation of the selectivity of the ISE was performed using the mixed solution method with log Kij values of Ca²⁺ > K⁺ > Mg²⁺ > Cu²⁺ > Fe³⁺ > Cr³⁺> Zn²⁺ > Cd²⁺. The Pb²⁺ ISE shows acceptable reproducibility and repeatability with standard deviation values of 0.065 and 0.0079, respectively. Fourier transform infrared (FT-IR) spectra confirmed that 1,10-phenanthroline was responsible for the formation of the Pb²⁺ ion entrapment via complexation. Other characterizations (crystallinity, micro-surface morphology, and mechanical strength) suggest the degradation of the membrane structure integrity after the application. The analysis results of Pb levels using the Pb²⁺ ISE in artificial and wastewater samples were not significantly different from the atomic absorption spectroscopy (AAS) measurement.

Herein, we report our success synthesizing silver nanoparticles (AgNPs) using aqueous extracts from the leaves and flowers of Calotropis gigantea growing in the geothermal manifestation Ie Seu-Um, Aceh Besar, Indonesia. C. gigantea aqueous extract can be used as a bio-reductant for Ag⁺→Ag⁰ conversion, obtained by 48h incubation of Ag⁺, and the extract mixture in a dark condition. UV–Vis characterization showed that the surface plasmon resonance (SPR) peaks of AgNPs-leaf C. gigantea (AgNPs-LCg) and AgNPs-flower C. gigantea (AgNPs-FCg) appeared in the wavelength range of 410–460 nm. Scanning electron microscopy energy-dispersive X-ray spectrometry (SEM-EDS) revealed the agglomeration and spherical shapes of AgNPs-LCg and AgNPs-FCg with diameters ranging from 87.85 to 256.7 nm. Zeta potentials were observed in the range of −41.8 to −25.1 mV. The Kirby-Bauer disc diffusion assay revealed AgNPs-FCg as the most potent antimicrobial agent with inhibition zones of 12.05 ± 0.58, 11.29 ± 0.45, and 9.02 ± 0.10 mm for Escherichia coli, Staphylococcus aureus, and Candida albicans, respectively. In conclusion, aqueous extract from the leaves or flowers of Calotropis gigantea may be used in the green synthesis of AgNPs with broad-spectrum antimicrobial activities.

A new electrochemical DNA biosensor based on mercaptopropionic acid (MPA)-capped ZnS quantum dots (MPA-ZnS QDs) immobilization matrix for covalent binding with 20-base aminated oligonucleotide has been successfully developed. Prior to the modification, screen-printed carbon paste electrode (SPE) was self-assembled with multilayer gold nanoparticles (AuNPs) and cysteamine (Cys). The inclusion of MPA-ZnS QDs semiconducting material in modified electrodes has enhanced the electron transfer between the SPE transducer and DNA leading to improved bioanalytical assay of target biomolecules. Electrochemical studies performed by cyclic voltammetry (CV) and differential pulsed voltammetry (DPV) demonstrated that the MPA-ZnS QDs modified AuNPs electrode was able to produce a lower charge transfer resistance response and hence higher electrical current response. Under optimal conditions, the immobilized synthetic DNA probe exhibited high selectivity towards synthetic target DNA. Based on the DPV response of the reduction of anthraquinone monosulphonic acid (AQMS) redox probe, the MPA-ZnS QDs-based electrochemical DNA biosensor responded to target DNA concentration from 1 × 10⁻⁹ μM to 1 × 10⁻³ μM with a sensitivity 1.2884 ± 0.12 µA, linear correlation coefficient (R²) of 0.9848 and limit of detection (LOD) of 1 × 10⁻¹¹ μM target DNA. The DNA biosensor exhibited satisfactory reproducibility with an average relative standard deviation (RSD) of 7.4%. The proposed electrochemical transducer substrate has been employed to immobilize the aminated Arowana fish (Scleropages formosus) DNA probe. The DNA biosensor showed linearity to target DNA from 1 × 10⁻¹¹ to 1 × 10⁻⁶ µM (R² = 0.9785) with sensitivity 1.1251 ± 0.243 µA and LOD of 1 × 10⁻¹¹ µM. The biosensor has been successfully used to determine the gender of Arowana fish without incorporating toxic raw materials previously employed in the hazardous processing conditions of polypyrrole chemical conducting polymer, whereby the cleaning step becomes difficult with thicker films due to high levels of toxic residues from the decrease in polymerization efficacy as films grew.

The research aims to evaluate the pollution of Pb and Zn in water, sediment, and Faunus ater samples collected from Krueng Balee (KB) and Kreung Reuleung (KR) Rivers, Aceh, Indonesia. The samples were collected at the upstream, midstream, and downstream of each river and analyzed using Atomic Absorption Spectrophotometry (AAS). The distribution of Pb and Zn pollution was analyzed using Principal Component Analysis (PCA). Our investigation revealed that the presence of Pb and Zn is still safe for water and sediment samples. Nevertheless, Pb and Zn contamination found in F. ater samples had exceeded the national safety limit for food. PCA analysis revealed correlations between samples suggesting the roles of physical and chemical properties of the river in the pollutant retainment. The analysis also indicated the possible antagonism between Pb and Zn accumulation in F. ater which has never been reported previously. We suggest routine monitoring of Pb and Zn concentrations. The role of the surrounding industry in the Pb and Zn pollution should be further studied.

Considering the significance of its demand around the world, the accurate determination of fish freshness with a simple and rapid procedure has become an interesting issue for the fishing industry. Hence, we aimed to fabricate a new optical pH sensor based on a polyelectrolyte (PEC) membrane of pectin–chitosan and the active material chromoionophore ETH 5294. A trial-and-error investigation of the polymer compositions revealed that the optimum ratio of pectin to chitosan was 3:7. With an optimum wavelength region (λ) at 610 nm, the constructed sensor was capable of stable responses after 5 min exposure to phosphate-buffered solution. Furthermore, the obtained sensor achieved optimum sensitivity when the PBS concentration was 0.1 M, while the relative standard deviation values ranged from 2.07 to 2.34%, suggesting good reproducibility. Further investigation revealed that the sensor experienced decreased absorbance of 16.67–18.68% after 25 days of storage. Employing the optimum conditions stated previously, the sensor was tested to monitor fish freshness in samples that were stored at 4 °C and ambient temperature. The results suggested that the newly fabricated optical sensor could measure pH changes on fish skin after 25 h storage at room temperature (pH 6.37, 8.91 and 11.02, respectively) and 4 °C (pH 6.8, 7.31 and 7.92, respectively).