Direct laser writing carbonization based on internal-reflection setup for fabricating shape-tailorable and sealed in-situ carbon features

•Experimental and FEA modelling study of the internal-reflection setup assisted direct laser writing carbonization process.•Establishment of the processing-structure relationship for the in-situ sealed carbon dots.•Identification of the local polymer matrix deformation and re-orientation associated with carbon dot formation.•Demonstration of the linear assembly of in-situ sealed carbon dots as sensitive piezoresistive sensor for underwater ultrasound sensing.