Method for measuring the concentration, the size and the zeta potential of nanoparticles in liquids in the scattered light mode and in the fluorescence mode, comprising the following features: a) a liquid sample containing nanoparticles in a sample container is irradiated from above with a laser beam via a beam splitter, a first liquid lens having an adjustable focus and an optical protection glass, wherein the nanoparticles, due to the Brownian movement, generate a scattered light fluctuating over time, and the sample-liquid-surface, the first liquid lens and the optical protection glass generate a partly reflected laser light which is directed via the same beam splitter and a second liquid lens having an adjustable focus to a detector, b) for observing the fluorescence light, a fluorescence filter is inserted into the convergent beam path between the second liquid lens and the detector for increasing a distance of the focal points between a scattered-light-plane and a fluorescence plane, wherein the laser proportion as part of the overall signal of the scattered light fluctuating over time and the partly-reflected laser light at the detector is determined by means of a measurement with a liquid without particulate content, wherein the concentration and the size of the nanoparticles is determined based on the proportion of the scattered light as part of the overall signal of the scattered light fluctuating over time and the partly-reflected laser light at the detector, wherein the zeta potential is determined based on an electrophoresis that is generated by means of first electrodes installed in the sample container and an undisturbed electrical field that is measured by means of second electrodes installed in the sample container, and wherein the control of the measurement process is performed with the help of a heterodyne 180 degree dynamic light scattering DLS program, an optics control for changing the focal length of the first and the second liquid lens (8, 9), and a display having a touch screen. a) a liquid sample containing nanoparticles in a sample container is irradiated from above with a laser beam via a beam splitter, a first liquid lens having an adjustable focus and an optical protection glass, wherein the nanoparticles, due to the Brownian movement, generate a scattered light fluctuating over time, and the sample-liquid-surface, the first liquid lens and the optical protection glass generate a partly reflected laser light which is directed via the same beam splitter and a second liquid lens having an adjustable focus to a detector, b) for observing the fluorescence light, a fluorescence filter is inserted into the convergent beam path between the second liquid lens and the detector for increasing a distance of the focal points between a scattered-light-plane and a fluorescence plane, wherein the laser proportion as part of the overall signal of the scattered light fluctuating over time and the partly-reflected laser light at the detector is determined by means of a measurement with a liquid without particulate content, wherein the concentration and the size of the nanoparticles is determined based on the proportion of the scattered light as part of the overall signal of the scattered light fluctuating over time and the partly-reflected laser light at the detector, wherein the zeta potential is determined based on an electrophoresis that is generated by means of first electrodes installed in the sample container and an undisturbed electrical field that is measured by means of second electrodes installed in the sample container, and wherein the control of the measurement process is performed with the help of a heterodyne 180 degree dynamic light scattering DLS program, an optics control for changing the focal length of the first and the second liquid lens (8, 9), and a display having a touch screen.