A microfluidic device comprising: a first fluid sample input port; a second fluid sample input port; a fluid exchange module in a first substrate, the fluid exchange module comprising a corresponding first microfluidic channel and a first array of island structures in the first microfluidic channel, the first array of island structures being arranged in one or more rows that extend along a longitudinal direction of the first microfluidic channel, each island structure in a row being spaced apart from an adjacent island structure in the row to form an opening, wherein a distance between a first wall of the first microfluidic channel and the first array of island structures progressively increases along a longitudinal direction of the first microfluidic channel, and a distance between a second wall of the first microfluidic channel and the first array of island structures progressively decreases along the longitudinal direction of the first microfluidic channel, wherein the first fluid sample input port is arranged closer to the first outer wall of the first microfluidic channel, and the second fluid sample input port is arranged closer to the second outer wall of the first microfluidic channel; and a particle concentration module in a second substrate, the particle concentration module comprising a corresponding second microfluidic channel and a second array of island structures, each island structure in the second array being spaced apart from an adjacent island structure to form an opening, wherein an output of the first microfluidic channel of the fluid exchange module is fluidly coupled to an input of the second microfluidic channel of the particle concentration module, or wherein an output of the second microfluidic channel of the particle concentration module is fluidly coupled to an input of the first microfluidic channel of the fluid exchange module, wherein the first substrate and the second substrate are the same substrate, and wherein a distance between a first wall of the second microfluidic channel and the second array of island structures progressively increases along a longitudinal direction of the second microfluidic channel, wherein the second array of island structures and a second wall of the second microfluidic channel are arranged to define an undulating fluid pathway between the island structures of the second array and the second wall along the longitudinal direction of the second microfluidic channel, and wherein a curvature of a second wall of the second microfluidic channel alternates between regions of high curvature and regions of low curvature. a first fluid sample input port; a second fluid sample input port; a fluid exchange module in a first substrate, the fluid exchange module comprising a corresponding first microfluidic channel and a first array of island structures in the first microfluidic channel, the first array of island structures being arranged in one or more rows that extend along a longitudinal direction of the first microfluidic channel, each island structure in a row being spaced apart from an adjacent island structure in the row to form an opening, wherein a distance between a first wall of the first microfluidic channel and the first array of island structures progressively increases along a longitudinal direction of the first microfluidic channel, and a distance between a second wall of the first microfluidic channel and the first array of island structures progressively decreases along the longitudinal direction of the first microfluidic channel, wherein the first fluid sample input port is arranged closer to the first outer wall of the first microfluidic channel, and the second fluid sample input port is arranged closer to the second outer wall of the first microfluidic channel; and a particle concentration module in a second substrate, the particle concentration module comprising a corresponding second microfluidic channel and a second array of island structures, each island structure in the second array being spaced apart from an adjacent island structure to form an opening, wherein an output of the first microfluidic channel of the fluid exchange module is fluidly coupled to an input of the second microfluidic channel of the particle concentration module, or wherein an output of the second microfluidic channel of the particle concentration module is fluidly coupled to an input of the first microfluidic channel of the fluid exchange module, wherein the first substrate and the second substrate are the same substrate, and wherein a distance between a first wall of the second microfluidic channel and the second array of island structures progressively increases along a longitudinal direction of the second microfluidic channel, wherein the second array of island structures and a second wall of the second microfluidic channel are arranged to define an undulating fluid pathway between the island structures of the second array and the second wall along the longitudinal direction of the second microfluidic channel, and wherein a curvature of a second wall of the second microfluidic channel alternates between regions of high curvature and regions of low curvature.