27 November 2009 New ICFO PhD Graduate

Dr. Manoj Mathew

Thesis Committee

Dr. Manoj Mathew obtained
his Doctoral Degree with a thesis on optical manipulation of neurons supervised by Prof. Pablo Loza-Alvarez.
Manoj Mathew holds a BTech in Electronics Engineering and an MTech in Photonics from the Cochin University of Science and Technology in India. He graduated from Cochin with a project on laser produced plasma from metallic targets, partly carried out during an internship at the University of California at San Diego, USA. In the fall of 2005, he joined ICFO at the group led by Prof. Pablo Loza-Alvarez to work in Neurophotonics, a research field that studies the various applications of light to neuroscience and medical neurology. Dr. Mathew’s focus has concentrated mainly on nano-neurosurgery and axonal guidance.

Manoj Mathew’s PhD thesis, “Neuron guidance and nano-neurosurgery using optical tools”, was supervised by ICFO Prof. Pablo Loza-Alvarez.


In recent years, light has emerged as a very powerful tool in the biomedical field for investigation, diagnosis, and therapies. The field of neuroscience and medical neurology has also benefited immensely from the use of these photonic tools. Axon guidance, for example, has been achieved by the use of CW light in contact with growth cones by exploiting light’s ability to impart forces.

Following this line of research, our investigation revealed the potential of a pulsed laser light placed at a certain distance to induce a signaling effect and hence attraction in axons of cortical neurons in-vitro. Laser light was focused through a microscope objective to a point placed at a distance of about 15µm from the growth cone. The experiments were performed using continuous wave (CW), chopped CW (20Hz), and mode-locked (FS) laser beams (80MHz) with 3mW of average power at the sample plane. In addition, a sham situation (no light beam) was used as a control. We found that CW light does not produce any significant influence on the axon growth. In contrast, when using pulsed light (chopped CW light or FS pulses), the beam was able to modify the trajectory of the axons, attracting approximately 45% of the observed cases to the beam spot. These results show that pulsed NIR laser light is capable of modulating the growth of axons in living cultured neurons. In the long term, this optically-based method has the potential to open up new alternatives to guide axons. It can be very helpful also in the search for therapies for neural degenerative disorders and injuries.

In order to exploit similar optically induced effects in-vivo, a new optical tool, the multimodal optical workstation, was developed. The basic motivation behind building this system was the development of a tool that could induce optical stimulation and at the same time image the results of the stimulation, in real time, using a multitude of imaging modalities. The workstation extends a commercially available confocal microscope (Nikon Confocal C1-Si) to include nonlinear/multiphoton microscopy and optical manipulation/stimulation tools such as nanosurgery. The setup allows both subsystems (confocal and nonlinear) to work independently and simultaneously. The workstation enables, for instance, confocal fluorescence microsopy, Laser Scanning Bright Field (LSBF) imaging and Second Harmonic Generation (SHG) imaging to be performed at the same time. The nonlinear microscopy capabilities are added around the commercial confocal microscope by exploiting all the flexibility offered by this microscope and without need for any mechanical or electronic modification of the confocal microscope systems.

The multimodal optical workstation was used for performing Nano-neurosurgery and observing the dynamics associated with the procedure by multimodal imaging of the procedure, in real time, using a multitude of imaging modalities. A number of effects that happen along with the process of nanosurgery, like spilling of axoplasm, laser induced muscular contraction, etc, were observed. A thorough assessment of collateral damage could also be performed. The ability of the multimodal system to assess collateral damage is much superior to the currently established ways of detecting collateral damage after Nano-neurosurgey. In addition SHG microscopy was introduced as a novel technique to detect collateral damage to the muscle surrounding the neurite targeted for Nano-neurosurgery.