On-Chip Holographic Microscopy and its Application for Automated Semen Analysis - Biomedical Optical Phase Microscopy and Nanoscopy - page 149

(A) (B)

Spatially incoherent light

D a ~100 µ m

Z a ~4 cm

Object plane
Sensor plane
(FOV ~24 mm 2 )

Z s ~1 mm

D a ( Z s / Z a )

Figure 8.1
(A) A lensless holographic on-chip microscope with dimensions of 4.2 cm 5.8 cm and

a weight of 46 g is shown with its sample-loading tray and a US quarter. A USB connection from
the side powers both the CMOS image sensor and the embedded light source (an LED filtered by
a pinhole). Both amplitude and phase images of the sperms can be generated with this compact
on-chip lensfree microscope over an FOV of 24 mm 2 with an effective NA of

4.2 cm

3 3

0.2. (B) The
relative positions of the light source, the semen sample, and the sensor chip are depicted with a
schematic diagram of the lensless holographic microscope shown in (A). This schematic drawing
is not to scale.

B

utilizes an incoherent or partially coherent light source (such as a light-emitting diode—
LED) that is filtered by a large aperture of, for example, B 0.1 mm to illuminate the sample
of interest as illustrated in Figure 8.1 . Over a short propagation distance of B 4 cm, this
illumination light picks up partial spatial coherence, after which it scatters from each cell to
coherently interfere with the background light, forming lensless holograms of the cells over
a large FOV ( B 24 mm 2 ). These lensless cell holograms can then be rapidly processed
(e.g., , 1 s) using a Graphics Processing Unit to reconstruct their microscopic images
(both amplitude and phase [11] ) as illustrated in Figure 8.2 .

Among various applications of this lensfree holographic microscope [11 15] , automated

semen analysis is one that can especially benefit from this microscope's field portability
and high throughput. As an important routine in fertility clinics, semen analysis is
extensively practiced for evaluating male fertility [16] and preparing artificial insemination
[17] . Semen samples are put into a counting chamber and then the sperm are manually
counted through an optical microscope to determine the sperm concentration. Such visual
assessment, although quite labor intensive, is still the gold standard that is not only
recommended by the World Health Organization (WHO) but also widely used in most
semen processing laboratories [18] . Several optical approaches, including turbidimetry