Jurnal Natural Vol. 21, (3) 2021 DOI 10.24815/jn.v21i3.22851 pISSN 1411-8513 eISSN 2541-4062 ORIGINAL RESEARCH Vol. 21 | No. 3 | October 2021 135 Optical pH sensor based on polyelectrolyte complex (PEC) pectin-chitosan/methanol anthocyanin extract of Catharanthus roseus for a new optical urea biosensor development NURHAYATI 1,3 , EKA SAFITRI 2 , KHAIRI SUHUD 2 , NAZARUDDIN NAZARUDDI 2 , BINAWATI GINTING 2 , MURNIANA MURNIANA 2 , SUSILAWATI SUSILAWATI 1 , SITTI SALEHA 1 AND SALSABILLA LATANSA NAZARUDDIN 4 1 Master of Science, Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Syiah Kuala, Banda Aceh 23111, Indonesia 2 Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Syiah Kuala, Banda Aceh 23111, Indonesia 3 Ship Engineering Department, Malahayati Merchant Marine Polytechnic, Aceh Besar, Aceh 23381, Indonesia 4 Faculty of Dentistry, Universitas Syiah Kuala, Banda Aceh 23111, Indonesia Abstract. Construction of optical pH sensor as a new platform optical urea biosensor based on polyelectrolyte complex (PEC) pectin-chitosan membrane and total phenolic (anthocyanin) of Tapak Dara flower (Catharanthus roseus) has been successfully carried out. The anthocyanin was extracted by a maceration method for 72 hours using methanol, and a total extract yield was 21.56% or 1.803 mg/L. Flavonoid and phenol tests showed positive results indicated by the formation of red and black colours. The anthocyanins showed maximum absorption at 578 nm for phosphate buffer and 575 nm for tris HCl buffer solution. The sensor fabrication was performed using a mixture of pectin and chitosan solutions with a ratio of 3:7. The anthocyanin was mixed into the solution with various concentrations. The sensor has an optimum sensitivity at the anthocyanin concentration of 0.05 mg/L (phosphate buffer) in the pH range of 7.0-9.5 and 0.025 mg/L (Tris HCl buffer) with a narrower pH range of 6.0-7.5. This sensor produced higher sensitivity, a wider linear range, and good linearity when it was exposed in 0.03M PBS. Reproducibility test with a relative standard deviation percentage (% RSD) was 9.20. The sensor showed a stable response after 5 minutes exposed to PBS solution, and it can be used to measure pH within the 20th day. The optimized optical pH sensor has been successfully developed as a urea optical biosensor by immobilizing urease on its surface. The biosensor showed a linear response in a series of 10 -1 -10 -10 M urea concentrations and has good linearity. Keywords: Anthocyanin, Catharanthus roseus optical pH sensor, polyelectrolyte pectin-chitosan, urea biosensor INTRODUCTION Sensors and biosensors are devices that still grab researchers attention to detect samples in various fields such as health, food, environment, and medicine. The devices have some advantages of being simple equipment and operation, sensitive, and selective. One of the sensors that continue to develop today is the pH sensor. Many sample measurements are based on the detection of pH. The monitoring of pH also is an indirect sample detection that used a concept enzyme and substrate reactions where the reaction produces H + or OH - ions. Some enzyme reactions with their substrate generate changes in pH, such as urease (1), alcohol oxidase (2), glucose oxidase (3), and peroxidase (4). Therefore, the need for a sensitive pH sensor to be further developed as a biosensor is still needed. A good performance optical pH sensor is promising to be developed as a *Corresponding Author: e.safitri@unsyiah.ac.id Received: September 2021 | Revised: October 2021 | Accepted: October 2021