Monika Janik

This study presents the first integration of nanodiamonds (NDs) with a microcavity in-line Mach-Zehnder interferometer (μIMZI) fabricated by femtosecond laser micromachining in the side surface of an optical fiber. NDs of different sizes form a structured and functional layer for receptor immobilization. Numerical analyses were performed to investigate how the ND particle size influences the optical field distribution in the cavity. The sensor's spectral response and refractive index sensitivity have been investigated experimentally. The results have shown that the ND layer enhanced light-surface interaction and increased the available area for binding, improving surface sensitivity and enhancing receptor loading. Among the tested configurations, the μIMZI modified with a 250 nm-thick ND layer exhibited the most favorable characteristics, achieving RI sensitivity of approximately 15,300 nm/RIU, and was therefore employed for specific, label-free detection of a model low-molecular-weight protein, green fluorescent protein (eGFP). The modified sensor demonstrated monotonic change and reproducible spectral response down to a protein concentration of 0.35 μg/mL, while the limit of detection was equal to 0.14 μg/mL, with a response time of about 30 minutes, which can be further optimized. In contrast, a non-modified reference μIMZI showed no response to comparable concentrations. Besides label-free detection, the multifunctional nature of NDs was further explored by exciting nitrogen-vacancy centers in the diamond structure, aiming for fluorescence-based sensing. These experiments confirmed that, in this configuration, the centers could be optically excited by a light guided through the fiber core, which is partially exposed within the microcavity and can interact directly with the ND-coated surface. The resulting fluorescence was detected from the microcavity region, demonstrating excitation and readout capabilities. Altogether, this work demonstrates that ND-based surface modification can simultaneously enhance sensitivity and expand the functional capabilities of these highly compact optical fiber biosensors.

Mercury, a toxic heavy metal produced through both natural and anthropogenic processes, is found in all of Earth’s major systems. Mercury’s bioaccumulation characteristics in the human body have a significant impact on the liver, kidneys, brain, and muscles. In order to detect Hg²⁺ ions, a highly sensitive and specific fluorescent biosensor has been developed using a novel, modified seven amino acid peptide, FY7. The tyrosine ring in the FY7 peptide sequence forms a 2:1 complex with Hg²⁺ ions that are present in the water-based sample. As a result, the peptide’s fluorescence emission decreases with higher concentrations of Hg²⁺. The FY7 peptide’s performance was tested in the presence of Hg²⁺ ions and other metal ions, revealing its sensitivity and stability despite high concentrations. Conformational changes to the FY7 structure were confirmed by FTIR studies. Simultaneously, we designed a miniaturized setup to support an in-house-developed micro-volume capillary container for volume fluorometry measurements. We compared and verified the results from the micro-volume system with those from the commercial setup. The micro-volume capillary system accommodated only 2.9 µL of sample volume, allowing for rapid, sensitive, and selective detection of toxic mercury (II) ions as low as 0.02 µM.

Mercury, a toxic heavy metal produced through both natural and anthropogenic processes, is found in all major Earth’s systems. Mercury's bioaccumulation characteristics in the human body have a significant impact on the liver, kidneys, brain, and muscles. In order to detect Hg2+ ions, a highly sensitive and specific fluorescent biosensor has been developed using a novel, modified seven amino acid peptide, FY7. The tyrosine ring in the FY7 peptide sequence forms a 2:1 complex with Hg2+ ions that are present in the water-based sample. As a result, the peptide's fluorescence emission decreases with higher concentrations of Hg2+. The FY7 peptide's performance was tested in the presence of Hg2+ ions and other metal ions, revealing its sensitivity and stability despite high concentrations. Conformational changes to the FY7 structure were confirmed by FTIR studies. Simultaneously, we designed a miniaturized setup to support an in-house-developed micro-volume capillary container for volume fluorometry measurements. We compared and verified the results from the micro-volume system with those from the commercial setup. The micro-volume capillary system accommodated only 2.9 µL of sample volume, allowing for rapid, sensitive, and selective detection of toxic mercury (II) ions ranging from 0.02 µM.

Spectroelectrochemical (SEC) measurements play a crucial role in analytical chemistry, utilizing transparent or semitransparent electrodes for optical analysis of electrochemical (EC) processes. The EC readout provides information about the electrode's state, while changes in the transmitted optical spectrum help identify the products of EC reactions. To enhance SEC measurements, this study proposes the addition of optical monitoring of the electrode. The setup involves using a polymer-clad silica multimode fiber core coated with indium tin oxide (ITO), which serves as both the electrode and an optical fiber sensor. The ITO film is specifically tailored to exhibit the lossy-mode resonance (LMR) phenomenon, allowing for simultaneous optical monitoring alongside EC readouts. The LMR response depends on the properties of the ITO and the surrounding medium's optical properties. As a result, the setup offers three types of interrogation readouts: EC measurements, optical spectrum analysis corresponding to the volume of the analyte (similar to standard SEC), and LMR spectrum analysis reflecting the state of the sensor/electrode surface. In each interrogation path, cyclic voltammetry (CV) experiments were conducted individually with two oxidation–reduction reaction (redox) probes: potassium ferricyanide and methylene blue. Subsequently, simultaneous measurements were performed during chronoamperometry (CA) with the sensor, and the cross-correlation between the readouts was examined. Overall, this study presents a novel and enhanced SEC measurement approach that incorporates optical monitoring of the electrode. It provides a comprehensive understanding of EC processes and enables greater insights into the characteristics of the analyte.

SPIE Digital Library Proceedings

Accurate and fast detection of viruses is crucial for controlling outbreaks of many diseases; therefore, to date, numerous sensing systems for their detection have been studied. On top of the performance of these sensing systems, the availability of biorecognition elements specific to especially the new etiological agents is an additional fundamental challenge. Therefore, besides high sensitivity and selectivity, such advantages as the size of the sensor and possibly low volume of analyzed samples are also important, especially at the stage of evaluating the receptor-target interactions in the case of new etiological agents when typically, only tiny amounts of the receptor are available for testing. This work introduces a real-time, highly miniaturized sensing solution based on microcavity in-line Mach–Zehnder interferometer (μIMZI) induced in optical fiber for SARS-CoV-2 virus-like particles detection. The assay is designed to detect conserved regions of the SARS-CoV-2 viral particles in a sample with a volume as small as hundreds of picoliters, reaching the detection limit at the single ng per mL level.