CytoDirect: the new era of cell counting

Cell counting is an important technique used in life science research, pharmaceutical R&D, diagnostic testing and more. Traditionally, this method is performed manually via microscope with cytotoxic reagents, or large, bulky automated cell counters — but what if there was a more convenient, safe and fast way to do this, all while maintaining a high level of accuracy?

METTLER TOLEDO’s newest product offering, CytoDirect, offers stain-free, automated cell counting in a portable device. CytoDirect leverages noninvasive technologies: digital holographic microscopy and machine learning algorithms. The advanced technology, together with an extra-large measurement area (31.2 mm²) and the elimination of cell staining, ensures measurement reliability in a short measurement time of only 15 seconds. A high degree of automation decreases human error, improves process standardization, and eliminates inter-operator variability.

Take it to your sample

CytoDirect is a portable device that enables semi-operator-independent cell counting, viability tests, and cell size distribution assessments at the actual work location (i.e. laminar flow hood, lab bench, in production). CytoDirect also follows the researcher anywhere in the lab thanks to its small footprint, Wi-Fi connection, and integrated battery. The device’s portability helps to further reduce the risk of cell culture contamination by minimizing user intervention and displacements across the workspace.

Say bye to trypan blue

Measuring cell viability typically involves additional biochemical procedures, such as staining to probe membrane intactness. This classical method involves extra incubation and handling steps with cytotoxic reagents, which increases error potential, experimental time, and operator exposure risk.

The unique combination of high-resolution digital holographic microscopy analyzed by a trained convolutional neural network allows reliable and reproducible cell analysis in a fully automated way¹ without staining.

CytoDirect uses the morphological and compositional differences between dead and living cells to determine culture viability. The digital holographic microscope can quantitatively assess changes in composition, e.g., reflecting protein turnover, making the percentage of viable cells directly accessible. This eliminates staining steps and reduces operation intervention to a minimum. Therefore, CytoDirect preserves the sample integrity and removes any cytotoxicity bias during the measurement.^2,3

The machine learning algorithm is trained to reliably evaluate a variety of cell lines, making it a useful tool for many applications in biopharma, biotech, and academic research.

The application note “Holographic Microscopy and Machine Learning: The Revolution of Cell Analysis” contains more information about digital holographic microscopy.

Ensured reliability

CytoDirect uses an extra-large measurement area — 30 times bigger than a standard hemocytometer — maximizing statistical significance in every measurement. Moreover, CytoDirect is robust and maintenance-free. It avoids wear-affected moving parts and does not require calibration.

The cell counting performance was assessed for many different cell types, including HeLa, PBMCs, and yeast, comparing linearity, accuracy, and reproducibility against manual counting using a hemocytometer. The experiments showed a high degree of linearity across the evaluated cell types. Therefore, it is shown that CytoDirect reliably detects and counts cells across a wide linear operating range, providing that it can be successfully applied in various cell-based experimental settings, ranging from established mammalian lines through primary cells to eucaryotic cells with walls. Moreover, CytoDirect shows higher precision than manual counting (Figure 1).

Figure 1: Precision comparison of CytoDirect and the hemocytometer in different cell concentrations.

Keep it simple

Operating CytoDirect is straightforward: the user pipettes 20 μL of a cell suspension without prior staining into the glass-made sample carrier. Then, the user can select an application (cell count or cell count and viability measurement). Guided by on-screen instruction, the user inserts the sample carrier in the adapter slot. The measurement starts automatically. Results are displayed after 15 seconds. The microscopic image can be displayed with a click, providing direct visual insight into the automatic detection of viable and dead cells, as shown in Figure 2.

Moreover, thanks to an integrated debris filter, CytoDirect easily recognizes cells vs. debris and other contamination, making the results even more reliable. The user still has the option to further filter the results by size by selecting the appropriate size range, as shown in Figure 2.

Figure 2: CytoDirect results display.

Connecting CytoDirect to LabX™ software will provide user management, store all measurements and metadata, and enable full GMP compliance in regulated environments such as biopharma.

The XDirect Portfolio

METTLER TOLEDO keeps innovating and adding additional life science tools, creating the XDirect portfolio, including (for now) CytoDirect and PlateDirect. PlateDirect A96 (Figure 3) features a robust, simplified, user-friendly plate reader and intuitive PC software that eliminates redundant features and moving parts. It provides everything needed to get ELISA, protein concentration, cell viability, or other absorbance measurements done while avoiding high capital, operational, and training costs.

Figure 3: PlateDirect A96.

The compact plate reader design allows you to run assays anywhere, share the device with colleagues, and easily stow it away when you are done. This efficiently uses lab space, minimizes contamination risks, and effectively promotes collaboration.

PlateDirect A96’s optical setup provides excellent optical accuracy and repeatability over a wide usable absorption range in the visible spectral region. As each well is measured with a dedicated photodiode, measuring a 96-well plate only takes 5 seconds.

The benefits of using METTLER TOLEDO’s CytoDirect and PlateDirect A96 are significant. CytoDirect provides a reliable, automated, and stain-free cell counting and viability testing solution. The instruments’ portability makes them ideal for various experimental settings while minimizing contamination risks and promoting collaboration. Overall, these devices offer a reliable and time-efficient cell analysis and plate reading solution.

_{1. Holographic Microscopy and Machine Learning – The Revolution of Cellular Assays, UserCom 28.}

_{2. Riss, Terry L., et al. “Cell viability assays.” Assay Guidance Manual [Internet]. Eli Lilly & Company and the National Center for Advancing Translational Sciences, 2016.}

_{3. Aslantürk, Özlem Sultan. In vitro cytotoxicity and cell viability assays: principles, advantages, and disadvantages. Vol. 2. InTech, 2018.}