Au/GQD hybrid interfaces: signal-transduction principles and evidence for metal-ion sensing

Gold/graphene quantum dot (Au/GQD) hybrids combine chemically accessible carbon surfaces with metallic, plasmonic, and emissive gold components. This review examines their interfacial signal-transduction principles and the available evidence for metal-ion sensing. Material descriptors, including surface functionality, morphology, electronic alignment, and spatial separation, are related to optical attenuation, fluorescence modulation, and electrochemical response. Examples from characterization, photocatalysis, and non-metal assays illustrate selected structural or transduction processes; they are distinguished from direct evidence of metal-ion recognition. The metal-ion studies are evaluated according to component roles, measured responses, analytical performance, and mechanistic support. Particular attention is given to plasmon-modulated Cr3+ fluorescence, Cu2+/Cd2+ ratiometric detection, and reaction-generated reporting of Au3+. Their comparison reveals heterogeneous recognition mechanisms and incomplete analytical benchmarking rather than a universally validated recognition pathway. A general hybrid advantage remains unestablished without matched component and alternative-material controls. Adjacent Au/GQD assays provide design hypotheses whose transfer requires target-specific binding and interference validation. Persistent limitations include unresolved signal origins, concentration-dependent matrix effects, inconsistent detection-limit reporting, and poorly standardized interface characterization. The resulting synthesis provides a structured basis for interpreting Au/GQD responses and identifying evidence needed to connect interfacial changes with reliable metal-ion detection.