Here, we present a protocol for standardized high-content imaging and data processing of propidium iodide (PI)/Hoechst 33342-stained cells to perform reproducible cell viability analysis using automated image acquisition and analysis workflows.
Method Article
Here, we present a protocol for standardized high-content imaging and data processing of propidium iodide (PI)/Hoechst 33342-stained cells to perform reproducible cell viability analysis using automated image acquisition and analysis workflows.
To address the challenges of low reproducibility due to operational variations in scientific research imaging and the complexity of analyzing a large number of samples using conventional methods, we introduce a protocol for staining HT22 cells with PI and Hoechst 33342 and then imaging and analyzing the data using the High-Content Imaging System. This workflow aims to establish robust imaging setting parameters and stringent quality control standards. It demonstrates the instrument's imaging settings and the workflow for three different image processing methods provided by the instrument: Multi-Wavelength Cell Scoring (Multi), Live-Dead (Live), and Custom Module Editor (CME). The image processing methods are compared and validated against the traditional method, ImageJ, to ensure their effectiveness. The study ultimately summarizes a workflow for using the High-Content Imaging System to determine cell viability using the PI and Hoechst double-staining method. By standardizing the entire imaging and data processing workflow, the study significantly enhances the reproducibility and reliability of scientific research imaging, thereby providing solid methodological support for cross-laboratory data comparison and advancing scientific research.
High-Content Imaging System serves as a crucial tool in modern scientific research, enabling high-speed imaging and multi-parameter assessment of injured or uninjured cells1,2,3. It plays an irreplaceable role in various disciplines. In the field of life sciences, it assists researchers in exploring the microscopic world of cells and tissues4,5. For instance, the precise detection of fluorescently labeled molecules and structures within cells allows clear visualization of cellular fine structures and dynamic changes6. In neuroscience research, it can perform three-dimensional imaging of neurons, aiding in the analysis of the complex connections and signal transduction mechanisms of neuronal networks, and providing crucial clues for understanding brain functions and the pathogenesis of neurological diseases7,8,9.
Despite the significant advantages of High-Content Imaging System technology, several issues remain with its imaging process. In the sample preparation stage, there is a high degree of subjectivity. In biological sample preparation, processes such as cell handling and staining lack relevant standards. In terms of imaging parameters, there are notable differences in exposure times and well plate selections across laboratories and high-content microscope models. In the data processing phase, there is a lack of standardization from noise reduction and contrast adjustment of raw images to the parameter identification and determination of target features. These issues directly lead to biases in microscope imaging results, causing a crisis of reproducibility.
This protocol uses a commercial cell line (HT22, ATCC) and does not involve human subjects or primary human tissues. No animals were used in this study.
1. Standardized sample preparation
2. Imaging specifications and parameter settings
3. Image processing and analysis
NOTE: This document outlines three image processing methods provided by the instrument’s companion software, all of which are suitable for the staining protocol used in this study. While these methods share the same underlying principle of recognition, they differ in specific processing techniques and types of data results. The same image processing workflow was as follows: Open the file → Load the original image with the corresponding processing method → Set the appropriate channel parameters → Generate a Mask → Set the measurement data type in Measure → Run the analysis → Observe the results → Export the data.
Impact of standardized preparation on imaging quality
The plate parameters were configured to ensure that the instrument could reliably locate the cell image layer. Samples prepared as a single layer of cells with moderate confluence facilitated image focusing at different objective magnifications and improved image recognition and quantitative analysis. Standardized sample preparation and optimized plate parameters effectively minimized edge effects, cell overlap, and other factors contributing to poor-quality imaging (Figure 1).
Comparison of the image calculation method functions
The PI/Hoechst 33342 double-staining method was used to distinguish live and dead cells. The Multi-Wavelength Cell Scoring, Live-Dead, and CME methods successfully processed these images by identifying objects based on fluorescence intensity and object size, whereas ImageJ identified objects based on grayscale values. The marking results obtained with these methods were generally comparable (Figure 3A–E).
The Multi-Wavelength Cell Scoring method required nuclear staining to identify all cells (Figure 4A). It can process up to 7 imaging channels and calculate parameters including cell count, area, and optical density.
The Live-Dead method was more flexible than the Multi-Wavelength Cell Scoring method. Both channels provide modules for nuclear staining, cytoplasmic staining or combined nuclear-cytoplasmic staining to identify all cells, live cells, or dead cells. The Split touching objects function separates overlapping objects, allowing calculation of cell count, area, and optical density. However, because it processed only dual-channel data, it was particularly well suited for PI/Hoechst 33342 double-stained cell viability assays (Figure 4B).
The CME method depended on user-defined image-processing logic. The number of processed channels corresponded to the number of acquired channels. The recognition results were refined using functions such as Fill Holes, Invert Objects, Grow Objects, Shrink Objects, Logical Operations, Remove Border Objects, Keep Marked Objects, Grow Objects without Touching, Mark Object Centers, Watershed, Remove Marked Objects, and Filter Mask to eliminate impurities and other sources of interference. This method also enabled the calculation of multiple object parameters for multidimensional analysis.
ImageJ did not process multiple channels simultaneously. For image batches with substantial background variation, manual processing and threshold adjustment were required, increasing subjectivity and reducing reproducibility.
Analysis of differences in processing results
A comparative analysis of the image-processing methods showed no significant differences in total cell counts, dead cell counts, or the dead-to-all-cell ratio among the Multi-Wavelength Cell Scoring, Live-Dead, CME, ImageJ, and traditional manual counting methods across 9 fields of view (Figure 5A–C, Supplementary File 1).
Similarly, no significant difference was observed in the ratio of dead-cell area to total cell area among the Multi-Wavelength Cell Scoring, Live-Dead, CME, and ImageJ methods. However, a significant difference was observed in the ratio of the average fluorescence intensity of dead cells to that of all cells among the Multi-Wavelength Cell Scoring, Live-Dead, and CME methods based on data obtained from 81 fields of view (Figure 5D–F).
Based on these findings, a standardized workflow for the High-Content Imaging System was established (Figure 6).

Figure 1: Low-quality imaging results. (A) The field of view is close to the well edge, revealing shadows from the well edge (BV2 cells in this case). (B) Arrows a and b indicate the overlap of cells in the DAPI channel and TL channel, with excessive cell confluency, and even a second layer or some floating cells. (C) The field of view has no cells; the plate parameters are incorrect; the focus is not on the cell layer, or the cells are not stained, resulting in no image in this field of view. Scale bar = 100 µm. Please click here to view a larger version of this figure.

Figure 2: Imaging parameter settings. (A) Arrow a indicates the bit depth icon. (B) Arrow b indicates the position of Shading Correction. Please click here to view a larger version of this figure.

Figure 3: Results of the same field of view identified by several methods. (A) Multi-Wavelength Cell Scoring mask results: the gray and red areas represent all cell nuclei identified in the DAPI channel, with the red area representing dead-cell nuclei identified in the Cy3 channel. (B) Live-Dead mask results: the green and red areas represent all cell nuclei identified in the DAPI channel, with the red area corresponding to dead-cell nuclei identified in the Cy3 channel. (C) CME mask result: the yellow and blue areas represent all cell nuclei identified in the DAPI channel, with the blue area corresponding to dead-cell nuclei identified in the Cy3 channel. (D) ImageJ mask result in DAPI. (E) ImageJ mask result in Cy3. Scale bar = 100 µm. Please click here to view a larger version of this figure.

Figure 4: Partial parameter setting pages. (A) The location indicated by a shows that the first channel of Multi-Wavelength Cell Scoring can only select the nucleus; (B) b and c indicate that Live-Dead can only process two channels, supporting PI/Hoechst 33342 double staining for dead and live cells. Please click here to view a larger version of this figure.

Figure 5: Differences in fluorescence image processing results. (A) Differences in all cell counts among the five processing methods. (B) Differences in dead cell counts among the five processing methods. (C) Differences in the ratio of dead cells to all cells among the five processing methods. (D) Differences in the ratio of dead cells to all cells among the four processing methods. (E) Differences in the ratio of dead cell area to all cell area among the four processing methods. (F) Differences in the ratio of the average fluorescence intensity of dead cells to that of all cells across the four processing methods. All error bars in the charts represent standard deviations. Please click here to view a larger version of this figure.

Figure 6: Standardized operation process. Workflow summarizing the standardized procedure for sample preparation, fluorescence staining, high-content imaging, image processing, image export, and data analysis. Please click here to view a larger version of this figure.
Supplementary File 1. Raw data for the cell count, area, and fluorescence intensity analysis presented in Figure 5. Please click here to download this file.
Using the PI and Hoechst double staining method to determine cell viability, for example, the high-content instrument can quickly and in a high-throughput manner calculate cell viability within the same batch using built-in algorithm modules. This method has several advantages, including low sample volume, low cost, minimal cell damage, weak fluorescence bleaching, resistance to quenching, and the ability to capture multiple images. Additionally, the imaging time for a 96-well plate is generally only 30–45 min20.
In the experimental protocol, to ensure imaging quality, focus on the following steps: First, ensure appropriate plate density to avoid excessive cell density, which can fill the image with cells, or insufficient density, which can wash cells away during staining and washing. Second, thoroughly wash the dye to prevent residual dye from affecting imaging. For cells with low adhesion, handle the addition and removal of liquid gently and slowly before and after staining, avoiding vertical addition. Use a side-wall addition to prevent the center of the field of view from losing cells, paying special attention to the detachment of dead cells during viability assays. Consider centrifuging the sample plate to reduce experimental errors if necessary. Third, choose an appropriate exposure time. Too long an exposure will increase the total imaging time and may miss the detection window, potentially leading to overexposure of some cells or background being recognized. Too short an exposure may result in incomplete image information, losing some characteristic details.
If a clear image cannot be found during imaging, trace the issue back to cell condition, dye residue, parameter settings, and other factors. During the experiment, if there are no cells at the bottom of the well, no image will be found in the field of view. If two or more uneven cell layers form at the bottom of the well, focusing becomes difficult, resulting in a blurry image. Excessive dye residue can lead to a strong background, making the target image less prominent. Large areas of dye residue can obscure cells in the field of view, while small particles of residue, similar in size to cells, can interfere with subsequent image recognition and segmentation. If the plate height and well height are not set according to the manufacturer's specifications for the 96-well plate, no image will be found in the field of view, or the sample position may shift, potentially damaging the objective lens.
Considering the flexibility and simplicity of operation, as well as the good data processing results, the optimal image processing module for the PI and Hoechst double staining method is Live-Dead. This program is specifically optimized for PI and Hoechst dyes and, compared to other methods and software, is simple to operate, calculates quickly, and allows easy batch-loading of images into the database with consistent parameter settings. The results are more comparable than those obtained with the currently common software, ImageJ. Different experimental modes can use corresponding proprietary methods or the Multi-Wavelength Cell Scoring general calculation mode; proprietary methods are more convenient, while the general calculation mode has fewer restrictions on staining methods. Different staining protocols require different optimal image processing modules. Develop computational methods tailored to experimental objectives. The ExportPro method for image export is simple and easy to learn, allowing for previewing reference objects. It is beginner-friendly, with a graphical interface that clearly explains parameter meanings and simplifies measurements, breaking down barriers to multi-software analysis and saving time on tool learning.
This study only validated a basic staining protocol. As a reference, other experimental protocols that differ significantly from this one still need to be validated against the new standard.
High-Content Imaging System serves as a core technology platform that integrates high-resolution imaging, multi-parameter synchronous detection, automated quantitative analysis, and high-throughput screening21,22,23. The integrated design of the device's imaging and calculation capabilities is expected to enable the development and establishment of corresponding experimental protocols and computational models for more existing imaging experiments7,24, ultimately improving the consistency and comparability of data obtained by different operators, at different times, and across batches.
All authors declare that there is no conflict of interest. During the translation of the manuscript, Zhipu AI was used solely for translation and not for generating research data, experimental results, or core academic content. The authors assume full responsibility for the content of the manuscript.
The authors thank the support provided by the Chengdu University of Traditional Chinese Medicine School Foundation. The authors thank the support from the MPRC2022034 grant. This funding is used to develop a 3D dynamic imaging method for intestinal bacteria in Erchen Decoction to treat simple obese mice. The authors acknowledge the research platform provided by the Chengdu University of Traditional Chinese Medicine Innovative Institute of Chinese Medicine and Pharmacy and the Institute of Interdisciplinary Studies.
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| 1.5 mL Centrifuge Tube | Labigic Technology Co., Ltd. | MCT-001-150 | |
| 1000 µL Pipette Tips | Labigic Technology Co., Ltd. | 35423003E | |
| 15 mL Centrifuge Tube | Labigic Technology Co., Ltd. | CT-002-15A | |
| 2.5 µL Pipette Tips | Qingdao Haier Biomedical Co., Ltd. | B10T | |
| 200 µL Pipette Tips | Labigic Technology Co., Ltd. | T-001-200 | |
| 50 mL Centrifuge Tube | Labigic Technology Co., Ltd. | CT-002-50A | |
| 96 Well Cell Culture Plate | Corning Incorporated | 3599 | |
| Adjustable Single-Channel Pipette, 0.1–2.5 μL | Eppendorf SE | 3120000216 | |
| Adjustable Single-Channel Pipette, 100–1000 μL | Eppendorf SE | 3120000267 | |
| Adjustable Single-Channel Pipette, 20–200 μL | Eppendorf SE | 3120000259 | |
| Adjustable Single-Channel Pipette, 2–20 μL | Eppendorf SE | 3120000232 | |
| Cell Culture Dish | Corning Incorporated | 430167 | |
| Cryogenic Vials | Labigic Technology Co., Ltd. | BS-20-ST | |
| Dimethyl sulfoxide (DMSO) | Beijing Solarbio Science & Technology Co., Ltd. | D8371 | |
| Dulbecco's Modified Eagle Medium (DMEM) | Life Technologies Limited | 11966-025 | In this study, the complete DMEM was prepared using 10% FBS, 1% Penicillin-Streptomycin Solution, and 89% DMEM. |
| ESCO CelCulture CO2 Incubator | Esco Micro Pte. Ltd. | CCL-170B-8 | |
| Fetal Bovine Serum (FBS,Superfine) | Procell Life Science & Technology Co.,Ltd. | 164210-50 | |
| Hoechst 33342 Fluorescent Dyes | Beijing Solarbio Science & Technology Co., Ltd. | B8040 | |
| HT22 cell | Procell Life Science & Technology Co.,Ltd. | CL-0697 | |
| ImageJ | National Institutes of Health | ImageJ is one of the image processing software used in the manuscript. | |
| ImageXpress Micro Confocal High-Content Imaging System | Molecular Devices, LLC | ImageXpress Micro Confocal | In the manuscript, use "High-Content Imaging System" as a substitute for the instrument name. |
| Low speed freezing centrifuge | Hunan Xiangyi Laboratory Instrument Development Co., Ltd. | L530R | |
| MetaXpress High-Content Image Acquisition and Analysis Software | Molecular Devices, LLC | The software is a companion to the ImageXpress® Micro Confocal High-Content Imaging System. In the manuscript, "The analysis software provided with the device" refers to this software. | |
| OptiMair Vertical Laminar Flow Cabinet | Esco Micro Pte. Ltd. | ACB-4E1 | |
| Parafilm M | Pechiney Plastic Packaging Inc. | PM996 | |
| PBS | Shanghai Yuchun biology science and technology co., ltd | YC-5013 | |
| Penicillin-Streptomycin Solution | Procell Life Science & Technology Co.,Ltd. | PB180120 | |
| Propidium Iodide Solution (PI) | Beijing Solarbio Science & Technology Co., Ltd. | C0080 | |
| Trypsin-EDTA Solution | BasalMedia Technology Co.,Ltd. | S310KJ |
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