Liquid Lenses open new perspectives for Microscopy

Abstract

The field of microscopy is now more developed than ever with a wide range of modalities such as fluorescence microscopy, OCT, and confocal microscopes, to name a few. Technical advances have significantly improved the image quality, size, and cost of such devices, thus making them available not only for industrial applications but also for researchers, universities, small laboratories and even the public. Image resolution and quality is of the utmost importance to analyze data from the observed samples. Optical systems in microscopy have a short working distance and a large numerical aperture, resulting in a narrow depth of field and the need to systematically refocus on the sample under study. This paper describes how the use of liquid lenses can greatly improve the imaging capabilities of microscopy devices while overcoming the limitations of bulk, cost, and robustness of traditional systems.

Introduction to liquid lenses 

Introduction to liquid lenses Inspired by the functionality of a human eye, liquid lenses offer manufacturers and OEMs improved speed and reliability over mechanical solutions. The human eye can adjust its focus to the environment at incredibly fast speeds; similarly, Corning’s liquid lenses emulate the eyes’ fluid and adaptable characteristics to create a rapid response to variable circumstances. This process is made possible by a technology called electrowetting, which uses an electrical signal to manipulate a liquid solution into a workable lens.

Traditional mechanical solutions are limited in their ability to deliver sharp images continuously and reliably. Corning® Varioptic® Lenses (Figure 1) offer innovative solutions to complex optical challenges. Varioptic Lenses enable fast focus and microfocus without moving parts. Traditional camera systems require moving parts which could begin to wear down and fail over the lifetime of the device. In comparison, liquid lenses function without the use of mechanically moving parts, eliminating much of the maintenance typically associated with vision systems.

Challenges in modern microscopy

In the field of microscopy there are today two main challenges:

- The first one concerns research microscopes that are built without constraints to observe the infinitely small. The challenge lies in the observation of nanoscopic samples scaling down to the atom level. Here, the size, cost and robustness of the equipment is not at stake and such devices are mainly used for research purposes.

- The second challenge lies in the continuous improvement of current microscopy setups regarding their general constraints: bulk, cost, weight, energy consumption, robustness, speed…

The primary concern in the field of microscopy is image quality. Without a proper image, it is impossible to extract any visual information from the sample. Microscopes often have a very short working distance in the range of a few millimeters with large numerical apertures to capture the maximum amount of light. This results in an extremely narrow depth of field. Focus is generally achieved by translating the optical system with mechanical parts or complex electronics to maximize sharpness on the sample or scan a 3D volume. The axial resolution (in depth) depends on the accuracy of the translation which requires bulky, expensive, and fragile mechanical parts. This goes against the global trend to build more compact and robust optical devices with equally good optical performances at an affordable price. Additionally, the energy and time required to move the entire optical stack is in the order of a few tens of seconds which adds up to minutes, hours or even days for the analysis of many samples.

A recent review on portable microscopes published in Microscopy Today1 highlights the growing need for simple and robust methods to capture images at the microscopic scale. According to this paper, the impact of climate change or the study of neglected tropical diseases for instance, has led scientists to carry out extensive studies in remote places such as Antarctica or the Amazon Rainforest. Out on the field, not only the image quality is at stake but the bulk, the durability and the energy consumption of microscopy device are also critical. There is a global trend for designing robust and compact portable microscopes that can be used anywhere outside a lab.