Circulating tumor cells (CTCs) are cancer cells that are detached from the primary and metastatic tumor site and invade the bloodstream. Most importantly, CTCs are the key players in the development of metastasis. As one of the main components of liquid biopsy, they may significantly contribute to improvements in early cancer diagnosis, monitoring response to therapy, and predicting recurrence of the disease. Although identifying and analyzing CTCs offers the potential for a real-time liquid biopsy, their detection is associated with a number of challenges, which mainly stem from three sources: complexity of the CTCs, complexity of the media (blood), and performance of the detection assays. Particularly, low concentration of the CTCs and the presence of a vast population of hematopoietic cells in the blood make their detection technically complex. The heterogeneity of the target cells and not enough sensitivity of the measuring platforms are also among major technical challenges in CTC detection. Therefore, this review aims to give an update on various methods developed for CTC isolation, including chip-based assays and biosensors. The work will elucidate various challenges associated with the isolation and detection of CTCs and showcase the studies that aimed to tackle them. A number of available commercial platforms for CTC detection and hurdles associated with their widespread applications in clinical settings will also be discussed.

This study investigated the biological removal of heavy metals from mine tailings in Kazakhstan using acidophilic microorganism strains Acidithiobacillus ferrivorans 535 and Acidithiobacillus ferrooxidans 377. The experiments were conducted in shake flasks at pH 1.6, various temperatures (28 °C, 18 °C, and 8 °C), and 10% solid concentration (w/v). The results of inductively coupled plasma optical emission spectroscopy and X-ray diffraction analyses showed that arsenic was particularly efficiently removed at 28 °C. At this temperature, A. ferrooxidans 377 was more efficient at removal than the other strain. Meanwhile, A. ferrivorans 535 was more efficient than A. ferrooxidans 377 at 8 °C. One of the more significant findings to emerge from this study is that arsenic can be removed at a low temperature and high solid concentration. The results of this study support the idea that microorganisms can be used for removing arsenic via a combination of biooxidation and chemical methods.

Tumor cells release biomarkers, such as CD44, into circulation, offering a minimally invasive window into tumor biology. However, conventional analytical methods often lack the sensitivity and dynamic range needed to detect these markers reliably in complex biological samples. Here, we exploit graphene oxide-coated semi-distributed interferometry to fabricate an optical fiber biosensor for sensitive CD44 detection. To establish the proof-of-concept, we focus on CD44 because of its well-established role as a circulating biomarker in breast cancer. We functionalize the sensor surface with anti-CD44 antibodies, confirm successful biofunctionalization and antibody specificity through complementary surface characterization and immunological assays, and optimize the platform to achieve a wide dynamic range and a limit of detection of 175 aM. Validation using clinical serum samples from breast cancer patients demonstrated a higher signal for cancer patients than for the healthy group, while successful detection of soluble CD44 in urine further demonstrated the biosensor's compatibility with multiple biological matrices. These findings establish the graphene oxide-coated semi-distributed interferometric biosensor as a highly sensitive platform for CD44 detection in clinically relevant samples. The demonstrated performance, together with the adaptability of the underlying SDI sensing architecture, highlights its potential for future development toward the detection of other circulating biomarkers.