{"p"=>"Attention Deficit Hyperactivity Disorder (ADHD), a prevalent neurodevelopmental condition, urgently requires objective biomarkers to improve diagnostic precision and treatment monitoring. This systematic review evaluates the utility of task-state functional near-infrared spectroscopy (fNIRS) in identifying neurobiological biomarkers for ADHD in children and adolescents. Following PRISMA 2020 guidelines and a pre-registered protocol (PROSPERO: CRD42024612203), we systematically searched PubMed, PsycINFO, Scopus, and Web of Science (through February 4, 2025) using terms including \"NIRS\" and \"ADHD\", identifying 1,027 articles. Data on fNIRS parameters and diagnostic accuracy metrics were extracted, with study quality assessed via BIOCROSS criteria. Synthesis of 50 eligible studies revealed consistent prefrontal cortex (PFC) dysfunction in ADHD, particularly reduced right PFC activation during executive function tasks (Go/No-go, Oddball, Stroop). Machine learning models leveraging fNIRS data achieved >80% accuracy in distinguishing ADHD from typically developing controls, demonstrating high specificity. Notably, pharmacological interventions (e.g., methylphenidate) partially normalized PFC activation patterns. Task-state fNIRS holds significant potential in identifying ADHD biomarkers, particularly through its ability to detect prefrontal cortex dysfunction. However, clinical translation requires addressing heterogeneity in task paradigms, standardization of fNIRS protocols, and validation across diverse populations. This review underscores the need for harmonized methodological frameworks to advance fNIRS from research to routine clinical practice in ADHD management."}