Vol.:(0123456789) 1 3 Applied Nanoscience https://doi.org/10.1007/s13204-020-01504-w ORIGINAL ARTICLE Green Synthesis of CuO nanoparticles via Plectranthus amboinicus leaves extract with its characterization on structural, morphological, and biological properties K. Velsankar 1  · V. Vinothini 1  · S. Sudhahar 1  · M. Krishna Kumar 2  · S. Mohandoss 3 Received: 30 May 2020 / Accepted: 1 July 2020 © King Abdulaziz City for Science and Technology 2020 Abstract Synthetic synthesis of nanoparticles is harmful to human and environment due to pollution. The use of harmful chemicals in synthetic method has avoided in the biosynthesis. To overcome the hurdles in synthesis of nanoparticles, the biogenic synthesis of CuO nanoparticles has been done with Plectranthus amboinicus leaf extracts. The biosynthesis provides the enhanced efficiency compared to synthetic methods. It establishes the environmentally friendly and pollution-free approach. The powder X-ray diffraction (XRD) pattern exhibited a crystalline nature with the crystallite size in 20–35 nm. The Fourier- Transform InfraRed (FTIR) spectrum explicated the Cu and O metal oxide bonds. The UV–visible analysis emphasized the stability of CuO nanoparticles with the inference of the Surface Plasmon Resonance band at 398 nm. The photoluminescence study displayed the bluish–green emission nature peak at 491 nm. The particle size analyzer manifested the synthesized CuO nanoparticles majority in 5–40 nm. The field-emission scanning electron micrographs (FESEM) and high-resolution transmission electron micrographs (HRTEM) exposed the spherical, circular-shaped nanoparticles with size in 5–30 nm range. The energy dispersive X-ray diffraction (EDAX) spectrum and mapping proved the CuO nanoparticles formation. The antimicrobial activity reported the potent nature of formed CuO nanoparticles on bacteria and fungi. The antioxidant activity identified the effective free-radical scavenging activity nature at 95% in 80 μg/mL and IC 50 value at 40.10 μg/mL concentration. The anti-inflammatory activity assessed the efficient nature of CuO nanoparticles in protein denaturation of Egg albumin at 92% in 500 μg/mL and IC 50 value at 243.08 μg/mL concentration. The anti-diabetic activity established the effective inhibition on α-Amylase at 94% in 500 μg/mL and IC 50 value at 317.19 μg/mL concentration. The anti-larvicidal activity manifested the potent inhibition on Anopheles subpictus mosquito larvae within 24 h in 100 ppm concentration and which exhibited low LC 50 value. Keywords CuO nanoparticles · Green synthesis · Antimicrobial activity · Antioxidant activity · Anti-diabetic activity · Anti-larvicidal activity Introduction Nanotechnology exhibits colossal achievement under research and practical applications. Its progressive behavior stimulates the researchers in the aspect of production and utilizing nanomaterials. The nanomaterials possessed char- acteristics which have much enticed the researchers. Inter- relating with bulk materials, the nanomaterials have attrac- tive properties in physical, chemical and biological aspects (Nabila et al. 2018; Chandra et al. 2019). The potent nature of its characteristics has much applied in the medical field from interconnection within biology and nanoscience. Its contribution now extended to all fields in every day-to-day practice (Vidovix et al. 2019). * S. Sudhahar sudhahars@alagappauniversity.ac.in; sudhaharmed@gmail.com 1 Department of Physics, Alagappa University, Karaikudi 630003, India 2 Department of Physics, Kalasalingam Academy of Research and Education, Krishnankoil 626126, India 3 School of Chemical Engineering, Yeungnam University, Gyeongsan, Gyeongbuk-do 38541, Republic of Korea