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➤ purpose, using the most efficient and cost-effective combination of optical components. We could economise on the design further by removing the 45° mirror, but we wanted to have the dual ability to look through the eyepiece as well as capturing digital images of the slide,’ Dr Zimic says.

‘The Peruvian health system pays for TB treatment and all the indirect costs associated. If we can reduce the time of TB diagnosis and determination of multi-drug resistance from 10 months to one week, we will have a very important impact on the prevalence of the disease,’ he concludes. Although this project began with TB, Dr Zimic explains that the same principle can be applied to any disease that could be diagnosed with pattern recognition on digital images. ‘We’ve developed other image recognition algorithms for intestinal parasites, malaria, and are currently working on cervical cancer to create automatic Papanicolau-smear slides,’ he says. Cervical cancer is a common form of cancer in women and, especially in rural areas in developing countries, diagnostic equipment is not available. Therefore, slides have to be shipped to designated laboratories, which takes time. Women might have to wait 4-5 months after a sample was taken before receiving the diagnostic results. ‘We want to do exactly the same thing [with cervical cancer] as we’re doing with TB,’ states Dr Zimic, ‘to bring the diagnostics of smears directly to the health centres. We’re currently developing the optical system and algorithm, in collaboration with the University of Washington in Seattle, for screening samples to reduce the number sent to pathology labs. This would help reduce the time taken for a complete diagnosis.’

Ultrafast spectroscopy Leaving the topic of microscopy for the moment and moving onto spectroscopy, researchers

disposal. Fluorescence provides a means of viewing proteins and cellular components; the expression of a fluorescently labelled protein, for instance, can be seen and tracked over time.

The KTN high-speed spectrometer, developed by NTT Photonics and supplied by AMS Technologies, scans a wide optical spectrum in microsecond-order timescales, ideal for observing ultrafast luminous phenomena

at NTT Photonics in Japan, which conducts photonics R&D mainly for telecommunications, have developed an optical beam scanner that’s used in a high-speed spectrometer. The spectrometer’s rapid scanning properties make it ideal for observing ultrafast luminous phenomena in bioanalytical science, among other potential applications. The scanner-based spectrometer, fabricated from potassium tantalate niobate (KTN), can measure a wide optical spectrum in microsecond-order timescales. AMS Technologies, based in Martinsried, Germany, will supply the KTN spectrometer, the technology surrounding which, as Dr Torsten Ledig, sales manager at AMS, explains is still under development. NTT Photonics based its scanner on a KTN crystal, a nonlinear crystal that can be used to deflect light beams from point to point at high frequency (megahertz) modulation. ‘The scanner operates at faster scanning frequencies compared to commercially available spectrometers,’ states Dr Ledig. ‘Solid-state spectrometers using CCD lines cannot make measurements over these timescales. Likewise, spectrometers using a slit and rotating the prism mechanically would also be much slower.’ With a standard spectrometer, the incident beam travels through a


prism or diffraction grating to split the light into different wavelengths. The dispersed light then passes through a slit and the wavelength- dependent signal is measured, typically either with a CCD line or a photomultiplier detector. This, however, is not very fast. NTT looked to develop an optic that would scan the beam in front of the dispersion element to achieve a different angle of incidence on the prism over time. ‘The slit and detector are in the same position and by scanning the incident light in front of the prism, the result is

When excited by one wavelength of light, fluorescent proteins, such as GFP, emit photons at a longer wavelength. ‘Fluorescence microscopes have to be able to separate the very intense excitation light from the very faint emitted light,’ explains Nicolas George, director of product marketing at US optics manufacturer Semrock. In modern microscopes, the excitation and emission light pass through part of the same optical system and are separated by a dichroic mirror. The mirror reflects the shorter excitation wavelengths coming back through the system and transmits only the longer emission signal. Semrock, the sister company of CVI Melles Griot, both of which are owned by Idex Corporation, supplies excitation filters, emission filters and dichroic mirrors used in fluorescence microscopes. The filters have very high blocking (optical density of six or seven) in all regions of the spectrum

The scanner operates at faster scanning frequencies compared to commercially available spectrometers

a wavelength-dependent signal detected over time,’ explains Dr Ledig.

The system developed by NTT is only a proof-of-principle device at the moment, according to Dr Ledig. So far, laser beams at specific wavelengths have been used as a light source to test the device, whereas, in reality, the spectrometer would be used to measure a fluorescence signal.

Fluorescence studies In the life science arena, fluorescence is one of the major tools scientists have at their

apart from a narrow band (approx ±10nm) around the wavelength of interest. The dichroic mirror has to have high reflectivity in the shorter wavelengths and then switch to high transmission in the longer wavelengths – the transmission profile is like a step function. Semrock supplies hard-coated filters for fluorescence microscopes. These are fabricated using ion- beam sputtering to deposit metal oxides on the glass. The technique produces a very dense and uniform coating. ‘Soft-coated filters are less expensive but have to be replaced over time,’ comments George. ‘The

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