Materials
1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) was purchased from Avanti Polar Lipids Inc. All lipids were stored at -20oC before use. L(+)-Ascorbic acid and 2-[4-(2-hydroxyethyl) piperazin-1-yl] ethane sulfonic acid (HEPES buffer salt) were purchased from Sigma-Aldrich. Chloroform (HPLC grade) was purchased from Fischer Scientific.
Methods
Preparation of Carbon Dots:
The carbon dots used in this paper were synthesized via the following procedure. Ascorbic acid (1.000 g) and deionized water (50 mL) was measured out and added to a 50 mL centrifuge tube. The ascorbic acid solution was first stirred for 15 minutes using a magnet stirrer, at room temperature, before vortex mixing for 1 min to ensure complete dissolution of the solute. The solution was then transferred to a teflon hydrothermal autoclave reactor liner, sealed tightly, and placed inside a hydrothermal autoclave reactor. The apparatus was then sealed tightly and placed in an oven set to 220oC for 48 hours. After 48 hours, the autoclave reactor was removed from the oven and allowed to cool to room temperature, at which point, the apparatus was opened, and the solution was transferred to a 50mL syringe and filtered using a sterile syringe filter with a 1 µm pore size to remove larger particulates. The
filtered sample was transferred to a refrigerator until further use.
Preparation of Phospholipid (POPC) Vesicles
POPC (1.14 mg) was dissolved in 60 µL of chloroform in a 25 mL pear-shaped flask. The chloroform was then removed by evaporation under a stream of nitrogen gas, followed by overnight drying under a high vacuum in a desiccator.
The next day, the dried POPC film was hydrated with 1000 µL of 10 mM HEPES buffer (pH 7.0). The sample was vortexed and subjected to multiple freeze-thaw cycles, alternating between freezing in liquid nitrogen (77 K) and thawing at room temperature. This process was repeated three to four times, with periodic vortexing and placement in an ice bath between cycles, until the sample became homogeneous. This preparation procedure promotes the formation of large unilamellar vesicles (LUVs).
Cenrifugation
The POPC control and the mixed POPC-CD samples are placed in 3kDa filter (Amicon) tubes and then centrifuged at a speed of 14,000 rpm for 15 minutes.
Dynamic Light Scattering (DLS)
DLS measurements were performed on a Zetasizer nano series (Malvern Instruments) at 25oC in disposable 40 uL micro cuvettes. Data were collected for 20s and averaged for 12 scans. The distance distribution is shown on a log scale using the Igor Pro software program (WaveMetrics)