A method for determining a property of nanoparticles in a flowing nanosuspension, comprising providing a sample comprising a flowing nanosuspension; non-invasively determining at least one of a size and a size distribution of nanoparticles of the flowing nanosuspension using Fourier domain, FD, low-coherence interferometry, LCI, wherein the determining comprises deriving a time, t, and optical path length, z, resolved LCI light scattering signal, I(t,z), from a t-resolved LCI wavelength spectrum of interference, and deriving information indicative of the at least one of the size and the size distribution of the nanoparticles from a z-resolved temporal autocorrelation function, G(τ,z), of I(t,z), in which τ represents a lag time; determining, from G(τ,z), z and τ-dependent decorrelation factors, g F (τ,z) related to the flow of the nanosuspension; determining, from G(τ,z), z- and τ-dependent autocorrelations, g B (τ,z), representative of Brownian motion of the nanoparticles; characterized in that the method further comprises: determining, from G(τ, z), a characteristic optical path length, Z ss, representative of a photon mean free path in the flowing nanosuspension, for which g B (τ,z) for z< Z ss in the nanosuspension are independent of z within a measurement noise; and determining, based on g B (τ,z) for z<Z ss in the flowing nanosuspension, an averaged autocorrelation function, <g B (τ)>, representative of single scattered light, and performing a photon correlation spectroscopy, PCS, analysis using <g B (τ)> to extract the information relating to the at least one of the size and the size distribution of the nanoparticles. providing a sample comprising a flowing nanosuspension; non-invasively determining at least one of a size and a size distribution of nanoparticles of the flowing nanosuspension using Fourier domain, FD, low-coherence interferometry, LCI, wherein the determining comprises deriving a time, t, and optical path length, z, resolved LCI light scattering signal, I(t,z), from a t-resolved LCI wavelength spectrum of interference, and deriving information indicative of the at least one of the size and the size distribution of the nanoparticles from a z-resolved temporal autocorrelation function, G(τ,z), of I(t,z), in which τ represents a lag time; determining, from G(τ,z), z and τ-dependent decorrelation factors, g F (τ,z) related to the flow of the nanosuspension; determining, from G(τ,z), z- and τ-dependent autocorrelations, g B (τ,z), representative of Brownian motion of the nanoparticles; characterized in that the method further comprises: determining, from G(τ, z), a characteristic optical path length, Z ss, representative of a photon mean free path in the flowing nanosuspension, for which g B (τ,z) for z< Z ss in the nanosuspension are independent of z within a measurement noise; and determining, based on g B (τ,z) for z<Z ss in the flowing nanosuspension, an averaged autocorrelation function, <g B (τ)>, representative of single scattered light, and performing a photon correlation spectroscopy, PCS, analysis using <g B (τ)> to extract the information relating to the at least one of the size and the size distribution of the nanoparticles. determining, from G(τ, z), a characteristic optical path length, Z ss, representative of a photon mean free path in the flowing nanosuspension, for which g B (τ,z) for z< Z ss in the nanosuspension are independent of z within a measurement noise; and determining, based on g B (τ,z) for z<Z ss in the flowing nanosuspension, an averaged autocorrelation function, <g B (τ)>, representative of single scattered light, and performing a photon correlation spectroscopy, PCS, analysis using <g B (τ)> to extract the information relating to the at least one of the size and the size distribution of the nanoparticles.