Counting photoactive cells

1. A cell counting device for estimating the number of photoactive cells in a sample, the device comprising:

a chamber for receiving the sample;

at least one light source to generate at least one pulse of light and to emit the at least one pulse of light towards a section of the chamber, wherein the section of the chamber comprises a sub-sample of the sample;

a light detector to receive light emitted from the sub-sample in response to receiving the at least one pulse of light and to generate an electronic signal associated with the received light; and

a controller configured to

estimate the number of photoactive cells in the sample by:

calculating and storing a variable fluorescence [F v ] values of each sub-sample in a predetermined number of sub-samples, by estimating a minimal fluorescence [F o ] of the sub-sample using regression analysis of a first part of the light signal, estimating a maximal fluorescence [F m ] of the sub-sample using regression analysis of a second part of the light signal, and subtracting F o from F m for each sub-sample;

calculating a mean of the stored F v values, and store a distance from the mean of each F v value to obtain a plurality of distances; and

integrate a distribution of the plurality of distances to provide an estimate of the number of photoactive cells in the sample.

2. The cell counting device according to claim 1 , wherein the at least one light source is configured to generate a plurality of pulses of light, and the light detector is configured to receive light from the sub-sample at time intervals less than the duration of each pulse of light to form a light signal, optionally wherein the at least one light source is configured to generate pulses of light having a frequency of between 10 Hz and 100 Hz and a duration of between 200 μs and 700 μs.

3. The cell counting device according to claim 1 , wherein the controller is configured to estimate the cell density of the sample by dividing the estimate of the number of cells by a volume of the sample, and wherein the controller is configured to perform an action if the estimated cell density is greater than a first cell density threshold.

4. The cell counting device according to claim 3 , further comprising a means for indicating to the user that the estimated cell density exceeds the first cell density threshold, wherein the action comprises controlling the indicating means, optionally wherein the indicating means comprises at least one of a display, an alarm and an indicator light.

5. The cell counting device according to claim 1 , wherein the cell counting device is coupled to a ballast water treatment system, and the controller is configured to perform an action comprising controlling the ballast water treatment system to eliminate live cells, or wherein the cell counting device is coupled to an external display device, and the controller is configured to perform an action comprising controlling the external display device to display a message.

6. The cell counting device according to claim 1 , further comprising an outlet in fluid communication with the chamber for draining the sample from the chamber, further comprising an inlet in fluid communication with the chamber, arranged such that water can continuously flow from the inlet, through the chamber, to the outlet in a first mode of operation, wherein the chamber comprises a removable blocking member for blocking the inlet or the outlet to allow a discrete sample to be measured in a second mode of operation, optionally further comprising a valve arranged in at least one of the inlet or the outlet operable to allow the cell counting device to alternate between the first mode of operation and the second mode of operation, wherein in the first mode of operation the valve is open, and in the second mode of operation the valve is closed.

7. The cell counting device according to claim 6 , wherein the controller is configured to calculate the variable fluorescence of the sub-sample while the cell counting device operates in the first mode of operation, and if the variable fluorescence is less than a first F v threshold and is greater than a second F v threshold being less than the first F v threshold, the controller is configured to close the valve and to switch the cell counting device to operate in the second mode of operation, optionally wherein if the estimated cell density exceeds a second cell density threshold less than the first cell density threshold, the controller is configured to switch the cell counting device to the first mode of operation from the second mode of operation, and increase a frequency at which the variable fluorescence of the sub-samples are calculated.

8. The cell counting device according to claim 1 , further comprising a stirrer configured to stir the sample, such that each sub-sample is exchanged with the sample.

9. The cell counting device according to claim 1 , wherein the cells are biological fluorophores, wherein the sample is ballast water, and the cells are phytoplankton.

10. The cell counting device according to claim 1 , wherein the cells comprise a photoactive organic dye.

11. The cell counting device according to claim 1 , wherein a volume of each sub-sample is between 0.5% and 50% of the sample volume.

12. A system comprising:

a ballast water treatment system; and

the cell counting device according to claim 1 ,

wherein the controller of the cell counting device is configured to estimate a cell density of the sample by dividing the estimate of the number of cells by a volume of the sample and to control the ballast water treatment system to activate a means for eliminating live cells if the estimated cell density exceeds a cell density threshold.