The present invention relates to a biosensor for detecting the presence and/or measuring the concentration of at least one biological agent, comprising a support on which a barcode is disposed, at least one area of which is functionalised by at least one aptamer capable of selectively immobilising said biological agent, said aptamer per se being directly or indirectly bonded to a pigment molecule capable either of producing colour, or of changing colour following the immobilisation of the biological agent by said aptamer.