A novel surface plasmon resonance sensor based on a D-shaped, all-glass, endless single-mode photonic crystal fiber is experimentally demonstrated in this paper, which provides a new approach to realizing a high-performance photonic crystal fiber surface plasmon resonance sensor. In order to achieve the best performance, the side-polished position of the D-shaped photonic crystal fiber is theoretically and experimentally obtained. The proposed sensor can be used in wavelength and intensity interrogations simultaneously, and the experimental results of wavelength interrogation agree well with theoretical results. By combining the two interrogation methods, we present a two-feature interrogation method to improve the resolution. As a new interrogation method, the two-feature resolution is determined to be 6.53 × 10 ⁻⁵ RIU, which is higher than those of the wavelength and intensity interrogations.

A highly sensitive and label-free fiber optic surface plasmon resonance (SPR) biosensor for specific detection of C-reactive protein (CRP) is proposed and demonstrated. We take dopamine as a cross-linking agent to immobilize the anti-CRP monoclonal antibody, which is an efficient and simple method for specific modification of the fiber optic SPR sensor. The modified sensor can successfully detect CRP specifically. We realize the fabrication of a disposable fiber optic SPR sensor for the CRP specific detection. Through optimizing the immobilization time of anti-CRP monoclonal antibody and the reaction time of antigen and antibody experimentally, the sensor shows a satisfactory linear response (R² = 0.97) to CRP concentration within the range from 0.01 to 20 μg/ml. Moreover, the highest CRP sensitivity is obtained at 1.17 nm per lg (μg/ml). With the advantages of simple structure and easy fabrication, our sensor is convenient to be batch produced and controlled with good consistency, which is especially suitable for the fabrication of disposable biosensor. It makes sense that our detection can effectively avoid the cross pollution caused by repeated use of the sensor.

Sensing characteristics of D-shaped photonic crystal fiber surface plasmon resonance sensors are investigated in this paper. The finite element method is used to study the influences of side-polished depths and sensing layer thicknesses on our sensors. The results show that the sensitivity increases with the increase of the sensing layer thickness but decreases a little with the increase of the side-polished depth in a certain range. The influences of the side-polished lengths on our sensors are studied experimentally. It is revealed that a short side-polished length is conducive to improving the performance of our sensors. The highest sensitivity of our sensors is obtained to be 7381.0 nm/RIU in the refractive index environment of 1.40–1.42, when the side-polished length is controlled at 10 mm. The novel D-shaped photonic crystal fiber surface plasmon resonance sensors will bring new vitality to the application of biochemistry.

The urgent necessity for highly sensitive diagnostic tools has been accentuated by the ongoing mpox (monkeypox) virus pandemic due to the complexity in identifying asymptomatic and presymptomatic carriers. Traditional polymerase chain reaction-based tests, despite their effectiveness, are hampered by limited specificity, expensive and bulky equipment, labor-intensive operations, and time-consuming procedures. In this study, we present a clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a-based diagnostic platform with a surface plasmon resonance-based fiber tip (CRISPR-SPR-FT) biosensor. The compact CRISPR-SPR-FT biosensor, with a 125 μm diameter, offers high stability and portability, enabling exceptional specificity for mpox diagnosis and precise identification of samples with a fatal mutation site (L108F) in the F8L gene. The CRISPR-SPR-FT system can analyze viral double-stranded DNA from mpox virus without amplification in under 1.5 h with a limit of detection below 5 aM in plasmids and about 59.5 copies/μL when in pseudovirus-spiked blood samples. Our CRISPR-SPR-FT biosensor thus offers fast, sensitive, portable, and accurate target nucleic acid sequence detection.