A lateral flow assay device for the detection of a target peptide in a liquid sample, wherein the target peptide is C-terminal crosslinked telopeptide type II collagen (CTX-II), the device comprising: (a) a solid support, (b) a sample pad for initially receiving and optionally pre-treating the sample at a first end of the solid support, (c) an absorbent pad at a second end of the solid support, (d) a conjugate pad comprising in a dry state a mobilizable conjugate of a particle and the target peptide, wherein the particle is a colloid gold nanoparticle, and wherein the target peptide conjugated to said particle is biotinylated and the particle comprises on its surface a biotin-binding protein, (e) a target peptide reaction membrane comprising, (i) a capture region comprising an immobilized first capture reagent against the target peptide, and (ii) optionally a control region comprising an immobilized second capture reagent against particle control conjugate, wherein the sample pad, the conjugate pad, the reaction membrane and the absorbent pad are mounted to the solid support to permit capillary flow from the sample pad to the reaction membrane through the conjugate pad, and wherein the loading of the particle with the target peptide is from about 20 % to about 55 % of the maximal loading capacity of the particle. (a) a solid support, (b) a sample pad for initially receiving and optionally pre-treating the sample at a first end of the solid support, (c) an absorbent pad at a second end of the solid support, (d) a conjugate pad comprising in a dry state a mobilizable conjugate of a particle and the target peptide, wherein the particle is a colloid gold nanoparticle, and wherein the target peptide conjugated to said particle is biotinylated and the particle comprises on its surface a biotin-binding protein, wherein the particle is a colloid gold nanoparticle, and wherein the target peptide conjugated to said particle is biotinylated and the particle comprises on its surface a biotin-binding protein, (e) a target peptide reaction membrane comprising, (i) a capture region comprising an immobilized first capture reagent against the target peptide, and (ii) optionally a control region comprising an immobilized second capture reagent against particle control conjugate, wherein the sample pad, the conjugate pad, the reaction membrane and the absorbent pad are mounted to the solid support to permit capillary flow from the sample pad to the reaction membrane through the conjugate pad, and wherein the loading of the particle with the target peptide is from about 20 % to about 55 % of the maximal loading capacity of the particle. (i) a capture region comprising an immobilized first capture reagent against the target peptide, and (ii) optionally a control region comprising an immobilized second capture reagent against particle control conjugate, wherein the sample pad, the conjugate pad, the reaction membrane and the absorbent pad are mounted to the solid support to permit capillary flow from the sample pad to the reaction membrane through the conjugate pad, and wherein the loading of the particle with the target peptide is from about 20 % to about 55 % of the maximal loading capacity of the particle. <EOS>