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Author's personal copy
McArthur revisited: fluorescence microscopes for field
David Jones1, Julius Nyalwidhe2, Laurence Tetley3and Michael P. Barrett3
1Department of Experimental Orthopaedics and Biomechanics, Philipps University, Baldingerst, 35033 Marburg, Germany
2Institute of Parasitology, University of Marburg, Germany
3Division of Infection & Immunity, University of Glasgow, Institute of Biomedical and Life Sciences, Glasgow G12 8QQ, UK
inventors. Among those that have is the ‘McArthur’. As a
student in the 1930s, John Norris McArthur wanted a
portable microscope to take on field trips. His rugged
pocket field microscope [Mcarthur, J. (1958) A new con-
cept in microscope design for tropical medicine. Am. J.
Trop. Med. Hyg. 7, 382–385] remains a classic of compact
design and performance, and has been used for malaria
diagnosis over several decades. The ‘McArthur’ has
dimensions of 102 ? 63 ? 51 mm (McArthur folded the
160 mm path length with a prism) and uses phase-con-
trast and specialised oil immersion objective lenses.
Later, a plastic version was developed and further
adapted for the Open University by Kirk & Sons, UK
[McArthur J. (1971) The McArthur microscope–open uni-
versity model. Trans. R. Soc. Trop. Med. Hyg. 65, 438].
Microbial diagnostics has, in recent years, turned to new
technologies. Immunological tests are increasingly wide-
taken from a patient remains the gold standard in the
diagnosis of many diseases. Microscopy, too, has moved on
since McArthur first designed his microscope. In particu-
lar, fluorescence allows the rapid visualization of appro-
priately stained organisms within a complex sample. In
microbial diagnostics, fluorescent probes have been useful
in the identification of Plasmodium-infected red blood cells
[1,2] and Mycobacterium tuberculosis [3–5]. Wehavedevel-
oped a test that identifies drug resistance in trypanoso-
miasis by taking advantage of fluorescent compounds that
enter drug-sensitive but not drug-resistant parasites .
An instrument was developed by QBC Diagnostics with
great hopes for improving diagnostics of a number of
diseases, including malaria [7,8] and trypanosomiasis
. In addition to using fluorescent chemicals that selec-
tively enter pathogens, it is also possible to use fluores-
cently tagged pathogen-specific antibodies that can, in
principle, be employed to bind specifically to any pathogen.
A novel fluorescence field microscope would have great
area by introducing a model that was useful in detecting
microfilariae . However, that model never received
Classical fluorescence microscopy suffers several draw-
backs. Light sources make microscope designs cumber-
some and inappropriate for field use. High-energy
mercury or other arc light sources, such as Xenon, that
use capacitors usually run at 50–100 watts, power that
is difficult to achieve by means of non-mains electricity
generators. The bulbs are notoriously delicate and only
(?200 hours). In addition, mercury lamp explosions are
a potential safety hazard, and mercury lamps require
Light-emitting diodes (LEDs) are transforming fluor-
escence microscopy. LEDs are more or less monochromatic
and emit light over a narrow bandwidth. LEDs produce
light in a similar way to other light sources, although
emitted light comes from the specific band gaps of the
semi-conductor used in producing LEDs rather than from
intense heating, as in the case of incandescent lamps. This
allows LEDs to run at a much lower temperature, to use
lower voltages and to consume very little power (<20 mW
is all that is needed for a single monochromatic LED
when light collection is efficient, enabling standard battery
operation). In addition, LEDs can have lifespans of
10,000 hours or longer and, being solid-state semiconduc-
tors, they are very robust and not susceptible to vibration.
The Cytoscience LED fluorescence field microscope
(Figure 1, inset) [11,12] is equipped with LEDs to give
bright-field and fluorescence emission; additionally, it can
be run on rechargeable batteries, which allow many hours
of use away from a power supply. The first model has a
Nichia LED at 472 nm, which makes it ideal for identifying
acridine orange and other dyes, including fluorescein
isithiocyanate (FITC). The design of this microscope
ensures that the optics are protected from humidity and
dust by encasing them in a hermetically sealed unit. The
flexible design includes standard interchangeable RMS
objective lenses and a variety of trans-illumination modes
that can be interchanged. Many of the controls are pre-
fixedsothatoperationis assimple aspossible;thereisonly
one focus control (the fine focus). A dark room is not
required because the optics are enclosed within the unit.
Figure 2 shows a typical output from a slide of Plasmo-
dium falciparum-infected erythrocytes stained with acri-
dine orange. Slides can be fixed if desired; however,
parasites in fresh blood are rapidly stained, and wet
smears can provide more or less instantaneous diagnosis
of malaria infection. The microscopes can also pick up
fluorescence from FITC-tagged antibodies, which enables
in situ diagnosis of any microbe for which a specific anti-
body is available.
a finiteamount of time
Corresponding author: Jones, D. (firstname.lastname@example.org).
Available online 7 September 2007.
TRENDS in ParasitologyVol.23 No.10
Author's personal copy Download full-text
The potential of fluorescence microscopy in pathogen
diagnosis was recognized many years ago, but its appli-
cation was hindered because of the impracticality of using
classical fluorescence microscopes in the field. We propose
here that LED field microscopes at last offer the potential
to use fluorescence microscopy as a diagnostic tool on a
wide-scale basis in the field.
Professor David Jones is Director of Cytoscience and invented the
Cytoscience field fluorescence microscope.
1 Kawamoto, F. (1991) Rapid diagnosis of malaria by fluorescence
microscopy with light microscope and interference filter. Lancet 337,
2 Chiodini, P.L., Moody, A.H. and Hunt-Cooke, A. (1991) Rapid diagnosis
of malaria by fluorescence microscopy. Lancet 337, 624–625
3 Kupper, T. et al. (1995) The cytologic diagnosis of Mycobacterium
kansasi tuberculosis by fluorescence microscopy of Papanicolaou-
stained specimens. Cytopathology 6, 331–338
4 Anthony, R.M. et al. (2006) Light emitting diodes for auramine O
fluorescence microscopic screening of Mycobacterium tuberculosis.
Int. J. Tuberc. Lung Dis. 10, 1060–1062
5 Steingart, K.R. et al. (2006) Fluorescence versus conventional sputum
smear microscopy for tuberculosis: a systematic review. Lancet Infect.
Dis. 6, 570–581
6 Stewart, M.L. et al. (2005) Detection of arsenical drug resistance in
Trypanosoma brucei with a simple fluorescence test. Lancet 366, 486–
7 Parzy, D. et al. (1990) The Quantitative Buffy Coat test (Q.B.C. test).
Monofluo Kit Falciparum. Comparative value in the rapid diagnosis of
malaria. Med. Trop. (Mars) 50, 97–102
8 Baird, J.K. et al. (1992) Diagnosis of malaria in the field by fluorescence
9 Ancelle, T. et al. (1997) Detection of trypanosomes in blood by the
Quantitative Buffy Coat (QBC) technique: experimental evaluation.
Med. Trop. (Mars) 57, 245–248
10 Shenoy, R.K. et al. (1996) The sheath of the microfilaria of Brugia
use on earth. Proc. Roy. Mic. Soc. 40, 91–96
12 Jones, D. (2003) Dynamic fluorescent imaging and photometry of cells
in microgravity. Proc. Roy. Mic. Soc. 38, 67–73
1471-4922/$ – see front matter ? 2007 Elsevier Ltd. All rights reserved.
Figure 1. Principles of LED epifluorescence microscopy. Light (green) of a given wavelength is emitted by a light-emitting diode (of which many now exist and which can
produce light over very narrow bandwidths). The light is directed by a dichroic mirror onto a sample that contains a fluorophore that emits light at a longer wavelength once
excited. This emitted light passes back through the objective lens and dichroic mirror and is viewed via the microscope eyepiece. A barrier filter prevents any light from the
excitation source from reaching the eyepiece; hence, only light emitted from the fluorescent marker is visible. Inset: the prototypical Cytoscience SA field Microscope
possesses an LED and bright-field set up. It is exceptionally compact and runs on rechargeable batteries.
Figure 2. Acridine orange-stained Plasmodium falciparum-infected red blood cells
viewed by the Cytoscience SA Field Microscope. P. falciparum-infected red blood
cells were stained with acridine orange (10 mM). A wet film of the cells was made
(fixation is not necessary, which greatly decreases preparation time for diagnosis
in comparison with classical staining methods such as Giemsa stain). The images
were taken through a x40 (NA 0.65) achromatic objective, further magnified x15 by
the camera optics. The fluorescence image is shown on the left (a). This image was
digitally added to a green light transmission image, and the composite image is
shown on the right (b). Scale bars = 10 mm.
TRENDS in ParasitologyVol.23 No.10469