A label-free microfluidic biosensor for activity detection of single microalgae cells based on chlorophyll fluorescence

Abstract

Detection of living microalgae cells is very important for ballast water treatment and analysis. Chlorophyll fluorescence is an indicator of photosynthetic activity and hence the living status of plant cells. In this paper, we developed a novel microfluidic biosensor system that can quickly and accurately detect the viability of single microalgae cells based on chlorophyll fluorescence. The system is composed of a laser diode as an excitation light source, a photodiode detector, a signal analysis circuit, and a microfluidic chip as a microalgae cell transportation platform. To demonstrate the utility of this system, six different living and dead algae samples (Karenia mikimotoi Hansen, Chlorella vulgaris, Nitzschia closterium, Platymonas subcordiformis, Pyramidomonas delicatula and Dunaliella salina) were tested. The developed biosensor can distinguish clearly between the living microalgae cells and the dead microalgae cells. The smallest microalgae cells that can be detected by using this biosensor are 3 μm ones. Even smaller microalgae cells could be detected by increasing the excitation light power. The developed microfluidic biosensor has great potential for in situ ballast water analysis.

Figure 1.

(a) The schematic diagram of the chlorophyll fluorescence detection system; (b) the dimensions of the microfluidic chip; and (c) the schematic diagram of the detection spot.

Figure 2.

Typical chlorophyll fluorescence signals of Karenia mikimotoi Hansen (a) individual living cells (b) dead cells (c) an enlarged view of a living cell signal. And (d) average chlorophyll fluorescence intensity of living and dead cells after being treated in darkness. The excitation light power is 2 mW and temperature is 21 °C.

Figure 2.

Typical chlorophyll fluorescence signals of Karenia mikimotoi Hansen (a) individual living cells (b) dead cells (c) an enlarged view of a living cell signal. And (d) average chlorophyll fluorescence intensity of living and dead cells after being treated in darkness. The excitation light power is 2 mW and temperature is 21 °C.

Figure 3.

Measured chlorophyll fluorescence of the living and dead microalgae cells of five microalgae species: (a) Platymonas subcordiformis; (b) Dunaliella salina; (c) P. delicatula; (d) N.closterium; and (e) Chlorella vulgaris. The excitation light power is 8 mW and the temperature is 21 °C.

Figure 3.

Measured chlorophyll fluorescence of the living and dead microalgae cells of five microalgae species: (a) Platymonas subcordiformis; (b) Dunaliella salina; (c) P. delicatula; (d) N.closterium; and (e) Chlorella vulgaris. The excitation light power is 8 mW and the temperature is 21 °C.

Figure 3.

Measured chlorophyll fluorescence of the living and dead microalgae cells of five microalgae species: (a) Platymonas subcordiformis; (b) Dunaliella salina; (c) P. delicatula; (d) N.closterium; and (e) Chlorella vulgaris. The excitation light power is 8 mW and the temperature is 21 °C.

Figure 4.

The relation between average chlorophyll fluorescence intensity of the microalgae cells (Chlorella vulgaris) and the power of the excitation light. Data are the averages [mean ± Standard Error (S.E.)] of twenty-one repeated measurements. Temperature is 21 °C.

Figure 5.

The response of chlorophyll fluorescence intensity of the microalgae cells (platymonas subcordiformis) to temperature. The excitation light power is 8 mW. Data are the average (mean ± S.E.) of twenty-one repeated experiments.