Optics and Photonics Journal, 2011, 1, 101-105
doi:10.4236/opj.2011.13017 Published Online September 2011 (http://www.SciRP.org/journal/opj)
Investigation of Laser Induced Inhibition and Simulation
in Biological Samples
Mohamed M. Fadhali1,*, Fadhl A. Saeed2, Nahlah M. Hashim1, Saktioto Toto3, Jalil Ali4
1*Department o f P hys ic s, Faculty of Science, Ibb University, Ibb, Yemen
2Department of Microbi olo gy, Faculty of Science, Ibb University, Ibb, Yemen
3Physcis Dept. Facult y of Mat h an d N atur al Sci ences, University of Riau, Indones ia
4Advanced Photonics Science Institute, Universiti Teknologi Malaysia, Johor, Malaysia
Received May 21, 2011; revised June 24, 2011; accepted July 2, 2011
Abstract
In this research, some experimental measurements have been carried out to study the biological effects in-
duced by laser irradiation on bacterial samples prepared by different ways and at different conditions. Con-
sidering the induced samples, the effect of laser irradiation has been investigated through analyzing some of
the properties of the transmitted and scattered laser beam for determining the stimulation or inhibition ex-
perienced by the investigated sample. In this study absorbance and scattering values have been measured as
indicators of sample response to the irradiation laser beam. Absorbance and scattering have been investigated
for different irradiation and sample parameters. Significant responses related to inhibition and stimulation
effects of the investigated samples have been obtained. These results may significantly contribute in deter-
mining the effective utilization of the laser beam as a therapeutic tool for accelerating the wounds and burns
healing of diabetic patients whom their response to anti-biotic is not appropriate. The simultaneous irradia-
tion of samples with the use of anti-biotic shows significantly positive effect and fast response.
Keywords: Photobiology, Inhibition, Stimulation, Absorption, Laser Therapy
1. Introduction
Lasers as highly stable sources of coherent and mono-
chromatic light, have been used extensively in technical
applications and for medical therapy. Laser light can
interact with tissue in four ways namely: transmission,
reflection, scattering and absorption. Transmission refers
to the passage of light through a tissue without having
any effect on that tissue or on the properties of the light.
The transmission of laser radiation in tissu es is related to
its wavelength. Reflection refers to the repelling of light
off the surface of the tissue without entering the tissue.
Scattering of light occurs after it has entered the tissue,
whereby the beam of light is spread out within the tissue
resulting in irradiation of a larger area than anticipated
[1-3]. Absorption is a process by which a photon gives
up energy to its surrounding medium. This energy is ul-
timately responsible for photobiostimulation [4,5]. The
effect of laser irradiation on biological objects depends
on experimental con ditions, su ch as the type of irradiated
cells, wavelength and intensity of light, etc. Laser was
first used in the medical field as a focused, high power
beam with photothermal effects in which tissue was va-
porized by the intense heat. It was postulated that surgi-
cal lasers normally have Gaussian beam modes. In such
mode the laser power is highest at the center of the beam
and falling off in a bell-shaped curve with the weakest
power at the periphery of the beam diffusing out into the
undamaged tissues [1,6]. This phenomenon was called
the “alpha-phenomenon” [4]. Laser devices were manu-
factured in which power densities and en ergy d ensities of
laser were lowered to a point where no photothermal
effects occurred but the photo-osmotic, photo-ionic and
photo-enzymatic effects were still operative. Applica-
tions of lasers are now widespread in almost every
medical specialty, especially dermatology, ophthalmol-
ogy and medical acupuncture [7].
The diverse tissue and cell types in the body all have
their own unique light absorption characteristics; that is,
they will only absorb light at specific wavelengths and
not at others. For example, skin layers, because of their
high blood and water content, absorb red light very read-

M. M. FADHALI ET AL. 102
ily, while calcium and phosphorus absorb light of a dif-
ferent wavelength [8]. Once a photobiological response
is observed, the next step should be to determine the op-
timum wavelength and dose of radiation to produce the
effect, i.e., an action spectrum. An action spectrum is a
plot of the relative effectiveness of different wavelengths
of light in causing a particular biological response, and
under ideal conditions it should mimic the absorption
spectrum of the molecule that is absorbing the light, and
whose photochemical alteration causes the biological
effect. Thus, an action spectrum not only identifies the
wavelength(s) that will have the maximum effect with
the least dose of radiation, but it also h elp s to iden tify th e
target of the radiation. For example, the action spectrum
for killing bacteria mimics the absorption spectrum of
deoxyribonucleic acid (DNA) [6,9-11]. This result is
understandable in view of the unique importance of
DNA to a cell.
Low-level laser Photobiology uses radiation both in
the visible (400 nm - 700 nm) and in the near-infrared
(700 nm - 1000 nm) regions of the spectrum. When a
photon is absorbed by a molecule, the electrons of that
molecule are raised to a higher energy state [7,8,12].
This excited molecule must lose its extra energy, and it
can do this either by re-emitting a photon of longer
wavelength (i.e., lower energy than the absorbed photon)
as fluorescence or phosphorescence, or it can lose energy
by giving off heat, or it can lose energy by undergoing
photochemical alteration.
Photobiological responses are the result of photo-
physical and/or photochemical changes produced by the
absorption of nonionizing radiation. Karu [6,13] has
shown that visible and near-infrared radiation is absorbed
in the respiratory chain molecules in the mitochondria
(e.g., cytochrome), which results in increased metabo-
lism, which leads to signal transduction to other parts of
the cell, including cell membranes, and ultimately to the
photoresponse (e.g., stimulation of growth) [8,12]. Laser
irradiation as a phototherapeutic modality for the induc-
tion or acceleration of wound healing was first intro-
duced by Mester et al. [4,14] in the 1970s but still is not
an established therapy. Th is is mainly due to the fact that
substantial amounts of research were originally done in
East European countries and published in non-peer-re-
viewed journals. Moreover, there has often been a lack of
accuracy in the documentation of exact irradiation pro-
tocols and the incorporation of appropriate controls in
the past. Additionally, the variety of laser systems and
experimental conditions utilized made comparison of
results difficult. Since more well-controlled studies have
been performed and since the Food and Drug Admini-
stration (FDA) has initiated research in the field of low
intensity laser therapy [1], this phototherapy is gaining
increasing interest.
2. Experimental Methods
This research work has been initiated by setting up the
experimental set up illustrated in Figure 1 which con-
sists of laser source, sample stage, optical detection cir-
cuit and magnetic stirrer.
This experimental setup has been designed for two
types of measurements, i.e. transmission and scattering
measurements. It consists of a laser, sample holder,
magnetic stirrer (to provide a homogeneous distribution
of the investigated sample), a photodetection circuit and
a display system (Multimeter and digital oscilloscope).
The samples were irradiated with (Diode Pumped
Solid State Laser) DPSS of output power of 50 mW &
150 mW and wavelength of 532 nm (green). The inves-
tigated samples were Catalase Enzyme and Staphylo-
coccus bacteria that are prepared with different concen-
trations using the common biological methods. The ex-
perimental results were based on the measurements of
the transmitted and/or scattered laser beam at different
angles.
3. Results and Discussions
3.1. Results for Catalase Enzyme
Catalase Enzymes samples are prepared with different
concentrations from yeast in cuvette with distilled water
and irradiated for different irradiation times. The detec-
tion process has been performed using H2O2. The ob-
tained results revealed that significant effect have been
occurred as shown in Figure 2. The reaction time is sig-
nificantly decreasing with the irradiation time. The reac-
tion time is depe ndent on the co ncen tration of the sample
and increasing with the sample concentration. However,
after a specific concentration the reaction time is de-
creasing with the irradiation time. In this case at a con-
centration of 0.6 g/mL the reaction time is greatest for all
irradiation times and drastically decreasing with the in-
Figure 1. Experimental setup.

M. M. FADHALI ET AL.103
Figure 2. Variation of reaction time with the irradiation
time for different sample concentration.
creasing of irradiation time for higher concentration as it
is clear for concentration of 0.8 g/mL which is depicted
in Figure 3. These results assured the applicability of
laser irradiation to stimulate Enzymes reaction concen-
tration. It also reveals that there will be an optimum
concentration that that exhibit significant response to the
laser irradiation. Moreover, the stimulation effect is en-
hanced with the increasing of irradiation time.
3.2. Bacteria Sample (Staphylococcus)
Samples (Staphylococcus injected into normal saline
solution) have been clinically collected and prepared in
different unit cell of formation (ucf). The samples were
put on a stirrer at 15 cm away from the laser source (la-
ser spot diameter 0.2 cm). The samples have been ar-
ranged in two different forms, i.e. on plates and/or in
cuvettes. The effects of irradiation with laser of 150 mW,
50 mW and wavelength of 532 nm on reaction time and
absorbance of the prepared samples have been studied
for different sample concentration. The obtained results
revealed that significant effect have been occurred. The
response was also investigated after each experimental
procedure using the convenient microbiological analysis
and inspections. It has been found that the change in ab-
sorbance and/or scattered laser in tensity was due to vari-
ation of one or more of the characters of bacterial sam-
ples, (such as viability or produced enzymes). It is there-
fore, quite amenable to take the variation in laser ab-
sorbance or scattered inten sity as ind icators to th e sample
response to the laser irradiation. As shown in Figure 4,
the absorbance of the laser beam is found to be strongly
dependent on the concentration of the sample and time of
irradiation. The inhibition effect was observed with in-
Figure 3. Variation of reaction time with the sample concen-
tration for different irradiation times.
Figure 4. Variation of absorbance with the concentration
for different irradiation time.
creasing irradiation time until certain irradiation time
(depending on the sample concentration), stimulation
effect is starting increasing with the increase of irradia-
tion time. Moreover, there is an optimum concentration
that exhibit best response as it is further illustrated in
Figure 5.
In both figures the variation of absorbance with irra-
diation time for different concentration or the variation
of absorbance with concentration for d ifferent irradiation
time, it can be clearly noticed that there is significant
variation for each case until certain specific irradiation
time and/or concentration at which the trend of response
is reversed. Meaning that by optimizing the aforesaid pa-
rameters, it is possible to control the required response.

M. M. FADHALI ET AL. 104
Figure 5. Variation of absorbance with the irradiation time
for different concentration.
A linear variation of absorbance with the irradiation
time was obtained when a laser power of 50 mw was
employed as shown in Figure 6. This means that there
was a response resulted in an inhib ition only without any
stimulation which is manifested by the decrease of ab-
sorbance with the irradiatio n time. This suggests that low
laser power can work better for wound healing in diabe-
tes patients.
On the other hand, the scattered laser intensity from
the irradiated sample has been also measured at the op-
timum irradiation time for different scattering angles as
depicted in Figure 7.
There is an optimum scattering angle (50 degree) at
which the scattered intensity is maximum and decreasing
below and above that angle. The scattered intensity is
also greatly affected by sample concentration and irra-
diation time (here the effect was best observed for irra-
diation time of 10 min.). Moreover, the possibility of
incorporating laser irradiation simultaneously with anti-
biotics as a therapeutic method for diabetic patients
whose response to antibiotic is very slow was investi-
gated with three different types of antibiotics, i.e., QB,
CB and ZX and the result is illustrated in Figure 8. It is
obvious that this procedure increases the impact effec-
tiveness of the antibiotics on the investigated samples
which is represented by the effective diameter range of
the implanted samples.
All those results mean that good selection and optimi-
zation of the process parameters such as laser wave-
length, intensity and th e time of irradiation with the type
of antibiotic is an important process to determine the
effectiveness of the medical treatment utilizing these
methods.
Figure 6. Variation of absorbance with the irradiation time
for a 50 mW laser power.
Figure 7. Variation of scattered intensity with the scattering
angle for different concentration s .
Figure 8. Variation of diameter of the effect range with
irradiation time.

M. M. FADHALI ET AL. 105
4. Conclusions
Enzyme catalase and Staphylococcus Bacteria samples
have been prepared in various concentrations and differ-
ent conditions. Th ey were irradiated for different irradia-
tion times with different laser beam characteristics. From
the obtained results, the photobiological stimulation and
inhibition was clearly demonstrated for both Enzymes
and Bacterial samples. That was clear from the absorb-
ance and scattering trends. However, for the case of low
laser power irradiation, it has been found that the irradi-
ated bacterial samples experienced only inhibition effect
which was obvious from the decreasing of absorbance
with the irradiation time. Moreover, the simultaneous
irradiation along with the anti-biotec incorporation shows
that the effectiveness of the anti-biotec was significantly
enhanced with the laser irradiation. The process of laser
irradiation as well as optimization of both laser beam
characteristics and samples conditions led to a conclu-
sion of the effectiveness of laser irradiation on the inves-
tigated samples which means that this method with the
required optimization can eventually be an effective
therapeutic tool for many diseases especially for wound
healing of diabetic patients. Moreover, further develop-
ment of this technique can end up with an efficient tool
for cancerous and malignant diseases.
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