Robotic microscopy for everyone: the OpenFlexure microscope

Abstract

Optical microscopes are an essential tool for both the detection of disease in clinics, and for scientific analysis. However, in much of the world access to high-performance microscopy is limited by both the upfront cost and maintenance cost of the equipment. Here we present an open-source, 3D-printed, and fully-automated laboratory microscope, with motorised sample positioning and focus control. The microscope is highly customisable, with a number of options readily available including trans- and epi- illumination, polarisation contrast imaging, and epi-florescence imaging. The OpenFlexure microscope has been designed to enable low-volume manufacturing and maintenance by local personnel, vastly increasing accessibility. We have produced over 100 microscopes in Tanzania and Kenya for educational, scientific, and clinical applications, demonstrating that local manufacturing can be a viable alternative to international supply chains that can often be costly, slow, and unreliable.

Fig. 1.

Overview of the OpenFlexure Microscope design, in transmission bright-field configuration. The condenser mount houses an illumination LED and a plastic condenser lens, while the optics module sits below the stage and houses an objective lens, tube lens, and camera. The entire optics module is attached to the $z$-actuator, providing variable focus. Both the optics module and $x$-$y$ stage are controlled by actuator gears at the back of the microscope, optionally driven by stepper motors. A detachable electronics housing stores optional electronic parts, such as motor controllers and a Raspberry Pi, for automation.

Fig. 2.

Cross-section schematics of trans- (a.) and epi- (b.) illumination configurations. LED1 provides transmission illumination, with a condenser lens L1. LED2 and lens L3 provide epi-illumination, connected to a removable filter cube housing two filters, F1 at $45°$ and F2. These filters can be removed or replaced by beamsplitters or polarizers to enable bright-field, fluorescence, or polarization-contrast epi-illuminated imaging. In both configurations, a standard RMS objective O1 and tube lens L2 image the sample onto the camera sensor CAM.

Fig. 3.

Schematics (left) and images (right) of four different imaging modalities possible using the OFM. a. Trans-illumination bright-field imaging of a Giemsa-stained thin blood smear, obtained with a $100\times$, $1.25$NA oil immersion objective. The inset shows a magnified section of the image, highlighting a ring-form trophozoite of Plasmodium falciparum. b. Epi-illumination bright-field imaging of a group of thin graphene flakes, obtained with a $40\times$, $0.65$NA dry objective. The inset shows a magnified section of the image, highlighting a resolvable tri-layer graphene flake (contrast has been digitally enhanced for clarity by increasing brightness and gamma). c. Polarisation-contrast trans-illumination image of 5CB liquid crystal droplets. A bright-field image is shown below for comparison. Both images were obtained with a $40\times$, $0.65$NA dry objective, and depict the same region of the sample. Arrows on the polarisers denote the transmission axis. d. Fluorescence images of unstained Lily of the Valley (convallaria majalis) rhizome, at two different wavelengths. The excitation wavelength (“Ex.”), and minimum emission wavelength imaged (“Em.”) are shown above the respective panels. Both images were obtained with a $40\times$, $0.65$NA dry objective, and depict the same region of the sample. Both the colour of illumination LED, and the filters in the filter cube, will change depending on the application.

Fig. 4.

Tiled scan image of a Giemsa-stained thin blood smear, obtained with a $100\times$, $1.25$NA oil immersion objective. The inset highlights an individual 8-megapixel image from the scan. The composite image was obtained from a $10\times 10$ grid of captures. After accounting for image overlap and skewing, and cropping out edges of the composite with missing sections, the resulting image is $14920$ px $\times 11270$ px ($\approx 170$ megapixel).