Recently, the wide spread of COVID-19 pandemic around the world has greatly affected human's daily life and economic development, which has aroused more human attention to health and safety [[1], [2], [3]]. In particular, COVID-19 infection towards human caused by cold chain products appeared, as the COVID-19 virus (SARS-COV-2) can survive and remain active under low temperature for longer time period (weeks to months) [[4], [5], [6], [7]]. Once the infected person is involved in the cold chain food production, the virus will further contaminate foods and the surfaces of packaging materials [[8], [9], [10], [11]]. Cold chain logistics elimination methods include disinfectant elimination, plasma air and ozone. Plasma air method usually takes long time [ [12]]. Disinfectant agents are prone to get frozen under low temperature (−15 °C) and meanwhile, most residues themselves will contaminate aquatic products, fruits or vegetables [13]. Ozone method usually requires a generator and sealed chamber [14]. Even worse, it has been observed that below freezing point, a coverage of ice and/or frost layer may form on the surfaces of packing materials due to the coagulation of moisture under a humidity circumstance. Such that those viruses or germs covered below the ice layer could not be easily acted on with commonly used disinfection materials such as chemicals or gas molecules. Issues on the disinfection beneath ice and frost layers are important while rarely studied.

Deep ultraviolet (DUV) light irradiation with high energy photons has been proved as a powerful tool in disinfection and sterilization by breaking the DNA/RNA strands of bacteria and virus [15,16]. AlGaN-based DUV LEDs, the new generation solid-state DUV light source, are widely concerned and advances in higher efficiency have been achieved [ [[18], [19], [20], [21], [22], [23]]. DUV LEDs are able to operate at extremely low temperature (−30 °C), which promise the application in cold chain environments. In addition, by using an irradiation wavelength at 260–280 nm, no residual toxic substances, derivative toxic ozone or corrosion will take place [17]. Previous works had shown that the inactivation rate of virus and bacteria depends on the DUV irradiation dose in both air and water medium [[24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35]]. Recently, the efficient inactivation of COVID-19 virus on material surfaces by DUV LEDs have been confirmed with very short irradiation time (∼ 1 s) [23,[36], [37], [38], [39], [40]]. However, systematic studies on the complicated situation of ice layers, such as impurities, bubbles, grain boundaries or crystal plane [41], as well as the penetrating disinfection effects beneath by DUV irradiation are still lacking.

In this work, we proposed a high-power-density DUV LED irradiator coupled with ellipsoidal reflective condenser for rapid penetrating inactivation and disinfection of bacteria and virus through ice layers. High efficient and high power DUV LEDs were fabricated based on hydrogen elimination treatments. In order to achieve high power density over long irradiation distance, reflective condensers in various curved surfaces were proposed and studied. The transmittance and optical properties of ice layers in different structural states were systematically investigated. Disinfection effects of SARS-COV-2 virus by condensed DUV LED irradiator and meanwhile, the sterilization rates beneath various ice layers were studied. As a result, 99.99 % inactivation rate for Escherichia coli (E.coli) can be reached beneath 5 mm thickness clear ice and opaque ice. The rapid DUV penetrating inactivation and disinfection through ice layers provide highly efficient sterilization applications in the complicated conditions in the cold chain logistics.