Publications

Below you can find a list of my published journal and conference articles. Each publication is accompanied by a small abstract, BibTex code and a DOI/URL. The red stars (*) indicate joint authorship. A list of my publications can be also found on Google Scholar.

(For those who are interested in similar Jekyll-based academic websites: The publications list below has been generated using the Export option in JabRef, as shown here. The produced .html file has been used as the template of the publications.html, saved in the _layouts folder. You can find more about my website’s structure here).

Perez-Tirador, P, Papadimitriou KI, Powell, S and Hebden, JC, "Time domain optical imaging device based on a commercial time-to-digital converter", Review of Scientific Instruments, Vol. 92, October 2021.

[Abstract] [BibTeX][DOI]

Abstract: Time-domain diffuse optical imaging is a noninvasive technique that uses pulsed near-infrared light as the interrogation source to produce quantitative images displaying the variation in blood volume and oxygenation in the human brain. Measuring the times of flights of photons provides information on the photon pathlengths in tissue, which enables absolute concentrations of the oxygenated and deoxygenated forms of hemoglobin to be estimated. Recent advances in silicon electronics have enabled the development of time-domain systems, which are lightweight and low cost, potentially enabling the imaging technique to be applied to a far greater cohort of subjects in a variety of environments. While such technology usually depends on customized circuits, in this article, we present a system assembled from commercially available components, including a low-cost time-to-digital converter and a silicon photomultiplier detector. The system is able to generate histograms of photon flight times at a rate of 81–90 kS/s and with a sampled bin width of 54 ps. The linearity and performance of the system are presented, and its potential as the basis for a modular multi-detector imaging system is explored.

BibTeX:

@article{Perez2021time,
  title={Time domain optical imaging device based on a commercial time-to-digital converter},
  author={P{\'e}rez-Tirador, P and Papadimitriou, KI and Powell, S and Hebden, JC},
  journal={Review of Scientific Instruments},
  volume={92},
  number={10},
  year={2021},
  publisher={AIP Publishing}
}

Papadimitriou KI, Rosas, EV, Zhang, E, Cooper, RJ, Hebden, JC, Arridge, SR and Powell, S, "A dual wavelength spread-spectrum time-resolved diffuse optical instrument for the measurement of human brain functional responses ", Biomedical Optics Express, Vol. 11, May 2020.

[Abstract] [BibTeX][DOI]

Abstract: Near-infrared spectroscopy has proven to be a valuable method to monitor tissue oxygenation and haemodynamics non-invasively and in real-time. Quantification of such parameters requires measurements of the time-of-flight of light through tissue, typically achieved using picosecond pulsed lasers, with their associated cost, complexity, and size. In this work, we present an alternative approach that employs spread-spectrum excitation to enable the development of a small, low-cost, dual-wavelength system using vertical-cavity surface-emitting lasers. Since the optimal wavelengths and drive parameters for optical spectroscopy are not served by commercially available modules as used in our previous single-wavelength demonstration platform, we detail the design of a custom instrument and demonstrate its performance in resolving haemodynamic changes in human subjects during apnoea and cognitive task experiments.

BibTeX:

@article{Papadimitriou2020BOE,
  title={Dual wavelength spread-spectrum time-resolved diffuse optical instrument for the measurement of human brain functional responses},
  author={Papadimitriou, Konstantinos I and Rosas, Ernesto E Vidal and Zhang, Edward and Cooper, Robert J and Hebden, Jeremy C and Arridge, Simon R and Powell, Samuel},
  journal={Biomedical Optics Express},
  volume={11},
  number={7},
  pages={3477--3490},
  year={2020},
  publisher={Optica Publishing Group}
}

Papadimitriou KI, Hebden, JC, Arridge, SR and Powell, S, "A dual-wavelength spread spectrum-based spectroscopic system For time-domain near-infrared diffuse optical imaging ", Proc. SPIE Bios, Vol. 10874, March 2019.

[Abstract] [BibTeX][DOI]

Abstract: We advance our previous research on spread spectrum spectroscopy by adding spectroscopic functionality using a custom-made optical transceiver. The new transceiver module features a 680nm communications-grade verticalcavity surface-emitting laser (VCSEL) and matches the performance of commercial 10Gb/s optical transceivers, which allow for a sub-ns instrument response. The optical power of the VCSEL can be software-adjusted up to 2mW with ∼40μA driving current resolution. This module, combined with a commercially available Gigabit optical transceiver at 850nm, allows us to derive information about the optical properties of tissue-equivalent phantoms and the concentration of various haemodynamic parameters in in vivo measurements.

BibTeX:

@proceeding{Papadimitriou2019SPIE,
  author = {Papadimitriou, Konstantinos I and Hebden Jeremy C and Arridge Simon R and Powell Samuel},
  title = {A dual-wavelength spread spectrum-based spectroscopic system For time-domain near-infrared diffuse optical imaging},
  journal = {Proc.SPIE},
  year = {2019},
  volume = {10874},
  pages = {10874 - 10874 - 9},
  doi = {https://doi.org/10.1117/12.2507992}
}

Vasilakis N, Papadimitriou KI, Morgan H and Prodromakis T, "Modular Pressure and Flow Rate-Balanced Microfluidic Serial Dilution Networks for Miniaturised Point-of-Care Diagnostic Platforms", Sensors, MDPI, Vol. 19(4), February 2019.

[Abstract] [BibTeX][DOI]

Abstract: Fast, efficient and more importantly accurate serial dilution is a necessary requirement for most biochemical microfluidic-based quantitative diagnostic applications. Over the last two decades, a multitude of microfluidic devices has been proposed, each one demonstrating either a different type of dilution technique or complex system architecture based on various flow source and valving combinations. In this work, a novel serial dilution network architecture is demonstrated, implemented on two entirely different substrates for validation and performance characterisation. The single layer, stepwise serial diluter comprises an optimised microfluidic network, where identical dilution ratios per stage are ensured, either by applying equal pressure or equal flow rates at both inlets. The advantages of this serial diluter are twofold: Firstly, it is structured as a modular unit cell, simplifying the required fluid driving mechanism to a single source for both sample and buffer solution. Thus, this unit cell can be used as a fundamental microfluidic building block, forming multistage serial dilution cascades, once combined appropriately with itself or other similar unit cells. Secondly, the serial diluter can tolerate the inevitable flow source fluctuations, ensuring constant dilution ratios without the need to employ damping mechanisms, making it ideal for Point of Care (PoC) platforms. Proof-of-concept experiments with glucose have demonstrated good agreement between simulations and measurements, highlighting the validity of our serial diluter.

BibTeX:

@article{vasilakis2019modular,
  author={Vasilakis, Nikolaos and Papadimitriou, Konstantinos I and Morgan, Hywel and Prodromakis, Themistoklis},
  title = {Modular Pressure and Flow Rate-Balanced Microfluidic Serial Dilution Networks for Miniaturised Point-of-Care Diagnostic Platforms},
  journal = {Sensors},
  publisher = {Multidisciplinary Digital Publishing Institute},
  year = {2019},
  volume = {19},
  number = {4},
  pages = {911},
  doi = {https://doi.org/10.3390/s19040911}
}

Evans D^*, Papadimitriou KI^*, Vasilakis N, Pantelidis P, Kelleher P, Morgan H and Prodromakis T, "A Novel Microfluidic Point-of-Care Biosensor System on Printed Circuit Board for Cytokine Detection", Sensors, MDPI, Vol. 18(11), November 2018.

[Abstract] [BibTeX][DOI]

Abstract: Point of Care (PoC) diagnostics have been the subject of considerable research over the last few decades driven by the pressure to detect diseases quickly and effectively and reduce healthcare costs. Herein, we demonstrate a novel, fully integrated, microfluidic amperometric enzyme-linked immunosorbent assay (ELISA) prototype using a commercial interferon gamma release assay (IGRA) as a model antibody binding system. Microfluidic assay chemistry was engineered to take place on Au-plated electrodes within an assay cell on a printed circuit board (PCB)-based biosensor system. The assay cell is linked to an electrochemical reporter cell comprising microfluidic architecture, Au working and counter electrodes and a Ag/AgCl reference electrode, all manufactured exclusively via standard commercial PCB fabrication processes. Assay chemistry has been optimised for microfluidic diffusion kinetics to function under continual flow. We characterised the electrode integrity of the developed platforms with reference to biological sampling and buffer composition and subsequently we demonstrated concentration-dependent measurements of H2O2 depletion as resolved by existing FDA-validated ELISA kits. Finally, we validated the assay technology in both buffer and serum and demonstrate limits of detection comparable to high-end commercial systems with the addition of full microfluidic assay architecture capable of returning diagnostic analyses in approximately eight minutes.

BibTeX:

@article{evans2018novel,
  author = {Evans, Daniel and Papadimitriou, Konstantinos I and Vasilakis, Nikolaos and Pantelidis, Panagiotis and Kelleher, Peter and Morgan, Hywel and Prodromakis, Themistoklis},
  title = {A Novel Microfluidic Point-of-Care Biosensor System on Printed Circuit Board for Cytokine Detection},
  journal = {Sensors},
  publisher = {Multidisciplinary Digital Publishing Institute},
  year = {2018},
  volume = {18},
  number = {11},
  pages = {4011},
  doi = {https://doi.org/10.3390/s18114011}
}

Zafeiropoulos G^*, Papadimitriou KI^* and Drakakis E (2018), "Performance ANd ACcuracy in Electrical BioActivity Recordings (PANACEA): A High-Performance, Wireless, Multi-instrument for Potentiometric and Amperometric Recording of Biosignals", Measurement., June, 2018.

[Abstract][BibTeX] [DOI]

Abstract: This paper presents the design, testing and quantitative evaluation of a high-performance, low-power, portable multi-instrument (107x79mm^2), capable of recording important biosignals accurately and in real-time. This highly versatile system has the ability to transmit the captured bio-data back to the user either in a wired (HDMI cable) or wireless (ZigBee protocol) manner, depending on the targeted application. The biological information that can be recorded by the proposed instrument spans a wide range of bio-potentials and bio-amperometric signals. The proposed instrument is split into two complementary “sub-instruments”, where one is operating as the front-end device, responsible for the accurate, low-noise signal detection and transmission, while the second “sub-instrument” is operating as the “base station”, responsible for the collection and further processing of the captured data. For wired transmission (e.g to the user’s PC) the front end module can operate independently, however, for wireless transmission both “sub-instruments” are required (transmitter-base station architecture). For wireless transmission, each of the two “sub-instruments” is equipped with dedicated 2 Mbps ZigBee radio transceivers and both parts are controlled by a small area embedded FPGA module. The front-end device features two distinct sections: (a) a current/voltage to voltage section comprising six potentiometry and two transimpedance amplifier-based amperometry channels. These eight in total analogue channels are converted into digital form by means of a 24 bit, voltage input, Analogue-to-Digital Converter (ADC) and (b) a four channel, commercially available switched-capacitor-based ADC Integrated Circuit (IC), which converts input charge to digital data with 16 or 20 bit resolution at 3.125 kSPS. The paper presents a plethora of measured wired and wireless experimental results, corresponding to most well-known biomedical and other biological/physical signals including: EEG, ECoG, EMG, ECG, PPG, intracardiac atrial fibrillation (AF) signals, cell media/tissue biopotential, drosophila H1-cell spiking signals and pH sensing using commercially available electrodes. The portable/wearable poly-instrument is suitable for Intensive Care Unit (ICU), High Dependancy Unit (HDU) as well as home monitoring.

BibTeX:

@article{zafeiropoulos2018,
  author = {Zafeiropoulos, GC. and Papadimitriou, KI and Drakakis, EM},
  title = {Performance ANd ACcuracy in Electrical BioActivity Recordings (PANACEA): A High-Performance, Wireless, Multi-instrument for Potentiometric and Amperometric Recording of Biosignals},
  journal = {Measurement},
  year = {2018},
  doi = {10.1016/j.measurement.2018.05.115}
}

Papadimitriou KI, Dempsey LA, Hebden JC, Arridge SR and Powell S (2018), "A spread spectrum approach to time-domain near-infrared diffuse optical imaging using inexpensive optical transceiver modules", Biomedical Optics Express., May, 2018. Vol. 9(6) OSA.