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In this study, a simple, portable, unibody semi-flow injection system was coupled with a screen-printed electrode (SFI/SPE) for the on-site electrochemical screening of sibutramine (SBM) in food supplements. The SFI was fabricated by laser engraving acrylic plastic and was attached to a modified SPE with double-sided adhesive tape. The SPE was modified with a nanocomposite of nitrogen-doped graphene nanoflakes and carbon nanotubes synthesized using hydrothermal and ultrasonic methods. The morphological structure and electrochemical properties of the nanocomposite were thoroughly investigated. The portable SFI-SPE sensing system was designed to be interfaced with a smartphone. Sample solutions can be continuously injected into the sensing system using a plastic syringe and SBM is determined by square wave anodic stripping voltammetry, controlled by means of a smartphone. The developed sensing system displayed linear ranges from 0.010 to 10 μg mL⁻ 1 and 10-60 μg mL⁻ 1 with an LOD of 0.0035 μg mL⁻ 1 . The sensor delivered a response in a short time and demonstrated not only good reproducibility (RSDs ranging from 2.9 % to 4.9 % (n = 10)) and excellent resistance to interference but also high accuracy. The developed sensor was utilized for the screening and quantification of SBM in food supplements but the system could be used in a wider range of electrochemical (bio) sensor applications in the future., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)