With a rapid improvement of smartphone hardware and software, especially complementary metal oxide semiconductor (CMOS) cameras, many optical biosensors based on smartphone platforms have been presented, which have pushed the development of the point-of-care testing (POCT). Imaging-based and spectrometry-based detection techniques have been widely explored via different approaches. Combined with the smartphone, imaging-based and spectrometry-based methods are currently used to investigate a wide range of molecular properties in chemical and biological science for biosensing and diagnostics. Imaging techniques based on smartphone-based microscopes are utilized to capture microscale analysts, while spectrometry-based techniques are used to probe reactions or changes of molecules. Here, we critically review the most recent progress in imaging-based and spectrometry-based smartphone-integrated platforms that have been developed for chemical experiments and biological diagnosis. We focus on the analytical performance and the complexity for implementation of the platforms.

Detecting biomarkers is an efficient method to diagnose and monitor patients’ stages. For more accurate diagnoses, continuously detecting and monitoring multiple biomarkers are needed. To achieve point-of-care testing (POCT) of multiple biomarkers, a smartphone biosensor system with the multi-testing-unit (SBSM) based on localized surface plasmon resonance (LSPR) integrated multi-channel microfluidics was presented. The SBSM could simultaneously record nine sensor units to achieve the detection of multiple biomarkers. Additional 72 sensor units were fabricated for further verification. Well-designed modularized attachments consist of a light source, lenses, a grating, a case, and a smartphone shell. The attachments can be well assembled and attached to a smartphone. The sensitivity of the SBSM was 161.0 nm/RIU, and the limit of detection (LoD) reached 4.2 U/mL for CA125 and 0.87 U/mL for CA15-3 through several clinical serum specimens testing on the SBSM. The testing results indicated that the SBSM was a useful tool for detecting multi-biomarkers. Comparing with the enzyme-linked immunosorbent assays (ELISA) results, the results from the SBSM were correlated and reliable. Meanwhile, the SBSM was convenient to operate without much professional skill. Therefore, the SBSM could become useful equipment for point-of-care testing due to its small size, multi-testing unit, usability, and customizable design.

To achieve high sensitivity and multi-mode sensing characteristics based on the plasmon effect, we explored a high-sensitivity refractive index sensor structure with narrow linewidth and high absorption characteristics based on theoretical analysis. The sensor structure is composed of periodic asymmetric ring cavity array, spacer layer and metal thin-film layer. The reflection spectrum of this structure shows six resonance modes in the wavelength range from visible to near-infrared. The sensor performance was optimized based on the change of the sensor structure parameters combining the simulation data, and the results shown that this kind of asymmetric laminated structure sensor has good sensing performance. In theory, it can be combined with microfluidic technology to achieve sensing detection of diverse test samples, multi-mode and multi-component, which has great potential in the field of biosensing.

We report a method for fabricating periodic nanostructures on the surface of polydimethylsiloxane (PDMS) using laser interference lithography. The wave-front splitting method was used for the system, as the period and duty cycle can be easily controlled. Indium tin oxide (ITO) glass reveals favorable characteristics for controlling the standing waves distributed in the vertical direction, and was selected as the rigid substrate for the curing of the PDMS prepolymer, photoresist spin coating, and exposure processes. Periodic nanostructures such as gratings, dot, and hole arrays were prepared. This efficient way of fabricating large area periodic nanoscale patterns will be useful for surface plasmonic resonance and wearable electronics.

Nanoimprint technology is powerful for fabricating nanostructures in a large area. However, expensive equipment, high cost, and complex process conditions hinder the application of nano-imprinting technology. Therefore, double-layer self-priming nanoimprint technology was proposed to fabricate ordered metal nanostructures uniformly on 4-inch soft and hard substrates without the aid of expensive instruments. Different nanostructure (gratings, nanoholes and nanoparticles) and different materials (metal and MoS₂) were patterned, which shows wide application of double-layer self-priming nanoimprint technology. Moreover, by a double-layer system, the width and the height of metal can be adjusted through the photoresist thickness and developing condition, which provide a programmable way to fabricate different nanostructures using a single mold. The double-layer self-priming nanoimprint method can be applied in poor condition without equipment and be programmable in nanostructure parameters using a single mold, which reduces the cost of instruments and molds.